From: John 1:47-51
The Calling of the First Disciples (Continuation)
 Jesus saw Nathaniel coming to Him, and said to him, "Behold, an Israelite indeed, in whom is no guile!"  Nathaniel said to Him, "How do you know me?" Jesus answered him, "Before Philip called you, when you were under the fig tree, I saw you."  Nathaniel answered Him, "Rabbi, you are the Son of God! You are the King of Israel!  Jesus answered him, "Because I said to you, I saw you under the fig tree, do you believe? You shall see greater things than these."  And He said to him, "Truly, truly, I say to you, you will see Heaven opened, and the angels of God ascending and descending upon the Son of Man."
45-51. The Apostle Philip is so moved that he cannot but tell his friend Nathanael (Bartholomew) about his wonderful discovery (verse 45). "Nathanael had heard from Scripture that Jesus must come from Bethlehem, from the people of David. This belief prevailed among the Jews and also the prophet had proclaimed it of old, saying: `But you, O Bethlehem, who are little to be among the clans of Judah, from you shall come forth for me one who is to be ruler of Israel' (Micah 5:2). Therefore, when he heard that He was from Nazareth, he was troubled and in doubt, since he found that the announcement of Philip was not in agreement with the words of the prophecy" (St. John Chrysostom, "Hom. on St. John", 20, 1).
A Christian may find that, in trying to communicate his faith to others, they raise difficulties. What should he do? What Philip did--not trust his own explanation, but invite them to approach Jesus personally: "Come and see" (verse 46). In other words, a Christian should bring his fellow-men, his brothers into Jesus' presence through the means of grace which He has given them and which the Church ministers--frequent reception of the sacraments, and devout Christian practices.
Nathanael, a sincere person (verse 47), goes along with Philip to see Jesus; he makes personal contact with our Lord (verse 48), and the outcome is that he receives faith (the result of his ready reception of grace, which reaches him through Christ's human nature: verse 49).
As far as we can deduce from the Gospels, Nathanael is the first Apostle to make an explicit confession of faith in Jesus as Messiah and as Son of God. Later on St. Peter, in a more formal way, will recognize our Lord's divinity (cf. Matthew 16:16). Here (verse 51) Jesus evokes a text from Daniel (7:13) to confirm and give deeper meaning to the words spoken by His new disciple.
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.