John 1.35-39:
The next day again John was standing with two of his disciples, (36) and he looked at Jesus as he walked by and said, “Behold, the Lamb of God!” (37) The two disciples heard him say this, and they followed Jesus. (38) Jesus turned and saw them following and said to them, “What are you seeking?” And they said to him, “Rabbi” (which means Teacher), where are you staying? (39) He said to them, “Come and you will see.” (ESV)
This account from John’s gospel gives information of what took place when the first disciples met Jesus and spent a portion of an afternoon with him. All four gospels tell of the interactions and calling of some of the first disciples of Jesus, but these verses tell of how the first introductions to Jesus took place. The first two disciples who met Jesus were disciples of John the Baptist and one of them was Andrew. As the account continues, Andrew went and found his brother Simon and told him that they had found the Messiah. Andrew brought Simon to Jesus and Jesus gave him the name of “Cephas”, which means “Peter”. The other disciple of John the Baptist is thought by some scholars to be John, brother of James.
The disciples heard John the Baptist confirm that Jesus is the Lamb of God. John the Baptist had said this the day before with the additional statement of “who takes away the sin of the world.” It appears as though they were earnestly seeking to learn as much as they could about Jesus, because they heard what John the Baptist had been preaching and affirming. It is clear that after spending a portion of the afternoon with Jesus, Andrew was convinced. Jesus is the Messiah.
For these men, these early interactions with Jesus and the faith that will grow in their lives, will be part of a foundation of trust in Jesus as the Messiah, to the extent that they will abandon their lifework and follow Jesus when he calls them. The gospels of Matthew, Mark, and Luke fill in more of these early details.