In the first chapter of John, we find the beginning of the Ministry of Jesus. John the Baptist is calling on people to Repent and be Baptized. The priests, Levite, and Pharisees asked ‘Who art Thou?’ He told them, he was not the Christ, but the Christ was among them and would Baptize them in the Holy Spirit.
He was asked, Why do you preach, if you are not Him? ‘He said, I am the voice of one crying in the wilderness, Make straight the way of the Lord, as said the prophet Esaias.
‘Why do you Baptize?’ ‘I baptize with water: but there standeth one among you, whom ye know not; He who is coming after I is preferred before me, whose shoe’s latchet I am not worthy to unloose.’
The next day John saw Jesus: ‘Behold the Lamb of God, which taketh away the sin of the world. This is he of whom I said After me cometh a man which is preferred before me: for he was before me.’
‘He that sent me to baptize with water, the same said unto me, Upon whom thou shalt see the Spirit descending, and remaining on him, the same is he which baptizeth with the Holy Ghost. And I saw, and bare record that this is the Son of God.’
Andrew was one who heard John the Baptist proclaim Jesus as the Messiah, the anointed one. Andrew heard, saw, considered and believed, and brought his brother Simon to Jesus. Jesus changed Simons name, to Cephas, a stone.
Jesus, the next day went to Galilee and found Phillip, Phillip brought Nathaniel, who asked, ‘Can any good come out of Nazareth?’
Jesus had both a Word of Wisdom about Phillip, that he would accept and follow Jesus. With Nathanael, both a Word of Wisdom and a Word of Knowledge. He saw him under the fig tree and knew he would follow Him.
He told Nathanial, he would see the angels of God ascending and descending, from heaven, on the Son of Man, Jesus. (John 1:1-51)
Jesus picked these to follow Him, because He had the knowledge and wisdom from God, that they would be true believers.