From: John 1:35-42
The Calling of the First Disciples
 The next day again John was standing with two of his disciples;  and he looked at Jesus as He walked, and said, "Behold, the Lamb of God!"  The two disciples heard him say this, and they followed Jesus.  Jesus turned, and saw them following, and said to them, "What do you seek?" And they said to Him, "Rabbi" (which means Teacher), "where are You staying?"  He said to them, "Come and see." They came and saw where He was staying; and they stayed with Him that day, for it was about the tenth hour.  One of the two who heard John speak, and followed him, was Andrew, Simon Peter's brother.  He first found his brother Simon, and said to him, "We have found the Messiah' (which means Christ).  He brought him to Jesus. Jesus looked at him and said, "So you are Simon, the son of John? You shall be called Cephas" (which means Peter).
35-39. Through these words of the Baptist, these two disciples are moved by grace to approach the Lord. John's testimony is an example of the special graces God distributes to attract people to Himself. Sometimes He addresses a person directly by stirring his soul and inviting him to follow Him; at other times, as in the present case, He chooses to use someone close to us who knows us, to bring us to meet Christ.
The two disciples already had a keen desire to see the Messiah; John's words move them to try to become friends of our Lord: it is not merely natural curiosity but Christ's personality which attracts them. They want to get to know Him, to be taught by Him and to enjoy His company. "Come and see" (John 1:39; cf. 11:34)--a tender invitation to begin that intimate friendship they were seeking. Time and personal contact with Christ will be needed to make them more secure in their vocation. The Apostle St John, one of the protagonists in this scene, notes the exact time it took place: "it was about the tenth hour", roughly four in the afternoon.
Christian faith can never be just a matter of intellectual curiosity; it affects one's whole life: a person cannot understand it unless he really lives it; therefore, our Lord does not at this point tell them in detail about His way of life; He invites them to spend the day with Him. St Thomas Aquinas comments on this passage saying that our Lord speaks in a lofty, mystical way because what God is (in Himself or in grace) can only be understood through experience: words cannot describe it. We grow in this understanding by doing good works (they immediately accepted Christ's invitation and as a reward "they saw"), by recollection and by applying our mind to the contemplation of divine things, by desiring to taste the sweetness of God, by assiduous prayer. Our Lord invited everyone to do all this when He said, "Come and see", and the disciples discovered it all when, in obedience to our Lord, "they went" and were able to learn by personal experience, whereas they could not understand the words alone (cf. "Commentary on St John, in loc".).
40-41. The Evangelist now gives us the name of one of the two disciples involved in the previous scene; he will mention Andrew again in connection with the multiplication of the loaves (John 6:8) and the last Passover (John 12:22).
We cannot be absolutely sure who the second disciple was; but since the very earliest centuries of the Christian era he has always been taken to be the Evangelist himself. The vividness of the account, the detail of giving the exact time, and even John's tendency to remain anonymous (John 19:16; 20:2; 21:7,20) seem to confirm this.
"St John the Apostle, who pours into his narrative so much that is first-hand, tells of his first unforgettable conversations with Christ. `"Master where are you staying?" He said to them, "Come and see." They went and saw where He was staying; and they stayed with Him that day, for it was about the tenth hour.'
"This divine and human dialogue completely changed the life of John and Andrew, and Peter and James and so many others. It prepared their hearts to listen to the authoritative teaching which Jesus gave them beside the Sea of Galilee" ([St] J. Escriva, "Christ is Passing By", 108).
Those hours spent with our Lord soon produce the first results of apostolate. Andrew, unable to contain his joy, tells Simon Peter the news that he has found the Messiah, and brings him to Him. Now, as then, there is a pressing need to bring others to know the Lord.
"Open your own hearts to Jesus and tell Him your story. I don't want to generalize. But one day perhaps an ordinary Christian, just like you, opened your eyes to horizons both deep and new, yet as old as the Gospel. He suggested to you the prospect of following Christ earnestly, seriously, of becoming an apostle of apostles. Perhaps you lost your balance then and didn't recover it. Your complacency wasn't quite replaced by true peace until you freely said 'yes' to God, because you wanted to, which is the most supernatural of reasons. And in its wake came a strong, constant joy, which disappears only when you abandon Him" ([St] J. Escriva, "Christ Is Passing By", 1).
42. What was it like when Jesus looked at someone? From what He says here, He seems both imperious and tender. On other occasions His glance is enough to invite a person to leave everything and follow Him, as in the case of Matthew (Matthew 9:9); or He seems to be full of love, as in His meeting with the rich young man (Mark 10:21), or He seems angry or sad, because of the Pharisees' unbelief (Mark 2:5), or compassionate, towards the widow of Nain (Luke 7:13). He is able to move Zacchaeus' heart to conversion (Luke 19:5); and He Himself is moved by the faith and generosity of the poor widow who gave in alms everything she had (Mark 12:41-44). His penetrating look seems to lay the soul bare to God and provoke one to self- examination and contrition--as happened to the adulterous woman (John 8:10) and to Peter who, after denying Christ (Luke 22:61) wept bitterly (Mark 14:72).
"You shall be called Cephas": naming something is the same as taking possession of the thing named (cf. Genesis 17:5; 22:28; 32:28; Isaiah 62:2). Thus, for example, Adam when he was made lord of creation, gave names to creating things (Genesis 2:20). "Cephas" is the Greek transcription of an Aramaic word meaning stone, rock: therefore, St. John, writing in Greek, has to explain the meaning of the word Jesus used. Cephas was not a proper name, but our Lord put it on Peter to indicate his role as His vicar, which He will later on reveal (Matthew 16:16-18): Simon was destined to be the stone, the rock, of the Church.
The first Christians regarded this new name as so significant that they used it without translating it (cf. Galatians 2:9, 11, 14); later its translation "Peter" (Petros, Petrus) became current, pushing the Apostle's old name--Simon--into the background.
"Son of John": ancient manuscripts include variants, such as "son of Jona".
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.