An example of the grace of the Holy Spirit at work within the life and words of St. Seraphim of Sarov has been preserved for us. In November of 1831, a pious Orthodox Christian named Nicholas Motovilov met with Saint Seraphim, and recorded his conversation. The entire conversation can be found here: http://www.pravoslavie.ru/english/47866.htm
Below is an extract from the conversation:
"But how," I asked Father Seraphim, "can I know that I am in the grace of the Holy Spirit?"
"It is very simple, your Godliness," he replied. "That is why the Lord says: All things are simple to those who find knowledge (Prov. 8:9, Septuagint). The trouble is that we do not seek this divine knowledge which does not puff up, for it is not of this world. This knowledge which is full of love for God and for our neighbour builds up every man for his salvation.
"Nevertheless," I replied, "I do not understand how I can be certain that I am in the Spirit of God. How can I discern for myself His true manifestation in me?"
Father Seraphim replied: "I have already told you, your Godliness, that it is very simple and I have related in detail how people come to be in the Spirit of God and how we can recognize His presence in us. So what do you want, my son?"
"I want to understand it well," I said.
Then Father Seraphim took me very firmly by the shoulders and said: "We are both in the Spirit of God now, my son. Why don't you look at me?"
I replied: "I cannot look, Father, because your eyes are flashing like lightning. Your face has become brighter than the sun, and my eyes ache with pain."
Father Seraphim said: "Don't be alarmed, your Godliness! Now you yourself have become as bright as I am. You are now in the fullness of the Spirit of God yourself; otherwise you would not be able to see me as I am."
Then, bending his head towards me, he whispered softly in my ear: "Thank the Lord God for His unutterable mercy to us! You saw that I did not even cross myself; and only in my heart I prayed mentally to the Lord God and said within myself: 'Lord, grant him to see clearly with his bodily eyes that descent of Thy Spirit which Thou grantest to Thy servants when Thou art pleased to appear in the light of Thy magnificent glory.' And you see, my son, the Lord instantly fulfilled the humble prayer of poor Seraphim. How then shall we not thank Him for this unspeakable gift to us both? Even to the greatest hermits, my son, the Lord God does not always show His mercy in this way. This grace of God, like a loving mother, has been pleased to comfort your contrite heart at the intercession of the Mother of God herself. But why, my son, do you not look me in the eyes? Just look, and don't be afraid! The Lord is with us!"
After these words I glanced at his face and there came over me an even greater reverent awe. Imagine in the center of the sun, in the dazzling light of its midday rays, the face of a man talking to you. You see the movement of his lips and the changing expression of his eyes, you hear his voice, you feel someone holding your shoulders; yet you do not see his hands, you do not even see yourself or his figure, but only a blinding light spreading far around for several yards and illumining with its glaring sheen both the snow-blanket which covered the forest glade and the snow-flakes which besprinkled me and the great Elder. You can imagine the state I was in!
"How do you feel now?" Father Seraphim asked me.
"Extraordinarily well," I said.
"But in what way? How exactly do you feel well?"
I answered: "I feel such calmness and peace in my soul that no words can express it."
"This, your Godliness," said Father Seraphim, "is that peace of which the Lord said to His disciples: My peace I give unto you; not as the world gives, give I unto you (Jn. 14:21). If you were of the world, the world would love its own; but because I have chosen you out of the world, therefore the world hates you (Jn. 15:19). But be of good cheer; I have overcome the world (Jn. 16:33). And to those people whom this world hates but who are chosen by the Lord, the Lord gives that peace which you now feel within you, the peace which, in the words of the Apostle, passes all understanding (Phil. 4:7). The Apostle describes it in this way, because it is impossible to express in words the spiritual well-being which it produces in those into whose hearts the Lord God has infused it. Christ the Saviour calls it a peace which comes from His own generosity and is not of this world, for no temporary earthly prosperity can give it to the human heart; it is granted from on high by the Lord God Himself, and that is why it is called the peace of God. What else do you feel?" Father Seraphim asked me.
"An extraordinary sweetness," I replied.
And he continued: "This is that sweetness of which it is said in Holy Scripture: They will be inebriated with the fatness of Thy house; and Thou shalt make them drink of the torrent of Thy delight (Ps. 35:8). And now this sweetness is flooding our hearts and coursing through our veins with unutterable delight. From this sweetness our hearts melt as it were, and both of us are filled with such happiness as tongue cannot tell. What else do you feel?"
"An extraordinary joy in all my heart."
And Father Seraphim continued: "When the Spirit of God comes down to man and overshadows him with the fullness of His inspiration, then the human soul overflows with unspeakable joy, for the Spirit of God fills with joy whatever He touches. This is that joy of which the Lord speaks in His Gospel: A woman when she is in travail has sorrow, because her hour is come; but when she is delivered of the child, she remembers no more the anguish, for joy that a man is born into the world. In the world you will be sorrowful; but when I see you again, your heart shall rejoice, and your joy no one will take from you (Jn. 16:21-22). Yet however comforting may be this joy which you now feel in your heart, it is nothing in comparison with that of which the Lord Himself by the mouth of His Apostle said that that joy eye has not seen, nor ear heard, nor has it entered into the heart of man what God has prepared for them that love Him (I Cor. 2:9). Foretastes of that joy are given to us now, and if they fill our souls with such sweetness, well-being and happiness, what shall we say of that joy which has been prepared in heaven for those who weep here on earth? And you, my son, have wept enough in your life on earth; yet see with what joy the Lord consoles you even in this life! Now it is up to us, my son, to add labours to labours in order to go from strength to strength (Ps. 83:7), and to come to the measure of the stature of the fullness of Christ (Eph. 4:13), so that the words of the Lord may be fulfilled in us: But they that wait upon the Lord shall renew their strength; they shall grow wings like eagles; and they shall run and not be weary (Is. 40:31); they will go from strength to strength, and the God of gods will appear to them in the Sion (Ps. 83:8) of realization and heavenly visions. Only then will our present joy (which now visits us little and briefly) appear in all its fullness, and no one will take it from us, for we shall be filled to overflowing with inexplicable heavenly delights. What else do you feel, your Godliness?"
I answered: "An extraordinary warmth."
"How can you feel warmth, my son? Look, we are sitting in the forest. It is winter out-of-doors, and snow is underfoot. There is more than an inch of snow on us, and the snowflakes are still falling. What warmth can there be?"
I answered: "Such as there is in a bath-house when the water is poured on the stone and the steam rises in clouds."
"And the smell?" he asked me. "Is it the same as in the bathhouse?"
"No," I replied. "There is nothing on earth like this fragrance. When in my dear mother's lifetime I was fond of dancing and used to go to balls and parties, my mother would sprinkle me with scent which she bought at the best shops in Kazan. But those scents did not exhale such fragrance."
And Father Seraphim, smiling pleasantly, said: "I know it myself just as well as you do, my son, but I am asking you on purpose to see whether you feel it in the same way. It is absolutely true, your Godliness! The sweetest earthly fragrance cannot be compared with the fragrance which we now feel, for we are now enveloped in the fragrance of the Holy Spirit of God. What on earth can be like it? Mark, your Godliness, you have told me that around us it is warm as in a bath-house; but look, neither on you nor on me does the snow melt, nor does it underfoot; therefore, this warmth is not in the air but in us. It is that very warmth about which the Holy Spirit in the words of prayer makes us cry to the Lord: 'Warm me with the warmth of Thy Holy Spirit!' By it the hermits of both sexes were kept warm and did not fear the winter frost, being clad, as in fur coats, in the grace-given clothing woven by the Holy Spirit. And so it must be in actual fact, for the grace of God must dwell within us, in our heart, because the Lord said: The Kingdom of God is within you (Lk. 17:21). By the Kingdom of God the Lord meant the grace of the Holy Spirit. This Kingdom of God is now within us, and the grace of the Holy Spirit shines upon us and warms us from without as well. It fills the surrounding air with many fragrant odours, sweetens our senses with heavenly delight and floods our hearts with unutterable joy. Our present state is that of which the Apostle says; The Kingdom of God is not food and drink, but righteousness and peace and joy in the Holy Spirit (Rom. 14:17). Our faith consists not in the plausible words of earthly wisdom, but in the demonstration of the Spirit and power (cp. I Cor.2:4). That is just the state that we are in now. Of this state the Lord said: There are some of those standing here who shall not taste of death till they see the Kingdom of God come in power (Mk. 9:1). See, my son, what unspeakable joy the Lord God has now granted us! This is what it means to be in the fullness of the Holy Spirit, about which St. Macarius of Egypt writes: 'I myself was in the fullness of the Holy Spirit.' With this fullness of His Holy Spirit the Lord has now filled us poor creatures to overflowing. So there is no need now, your Godliness, to ask how people come to be in the grace of the Holy Spirit. Will you remember this manifestation of God's ineffable mercy which has visited us?"
"I don't know, Father," I said, "whether the Lord will grant me to remember this mercy of God always as vividly and clearly as I feel it now."
"I think," Father Seraphim answered me, "that the Lord will help you to retain it in your memory forever, or His goodness would never have instantly bowed in this way to my humble prayer and so quickly anticipated the request of poor Seraphim; all the more so, because it is not given to you alone to understand it, but through you it is for the whole world, in order that you yourself may be confirmed in God's work and may be useful to others. The fact that I am a Monk and you are a layman is utterly beside the point. What God requires is true faith in Himself and His Only-begotten Son. In return for that the grace of the Holy Spirit is granted abundantly from on high. The Lord seeks a heart filled to overflowing with love for God and our neighbour; this is the throne on which He loves to sit and on which He appears in the fullness of His heavenly glory. 'Son, give Me thy heart,' He says, 'and all the rest I Myself will add to thee (Prov. 23:26; Matt. 6:33),' for in the human heart the Kingdom of God can be contained."
"And so, your Godliness, I have now told you and given you a practical demonstration of all that the Lord and the Mother of God have been pleased to tell you and show you through me, poor Seraphim. Now go in peace. The Lord and the Mother of God be with you always, now and ever, and to the ages of ages. Amen. Now go in peace."
And during the whole of this time, from the moment when Father Seraphim's face became radiant, this illumination continued; and all that he told me from the beginning of the narrative till now, he said while remaining in one and the same position. The ineffable glow of the light which emanated from him I myself saw with my own eyes. And I am ready to vouch for it with an oath.