Second Sign, Second Confession

After Jesu' baptism by John he begins to gather his disciples. The first two, John and Andrew, were disciples of John who now begin to follow Jesus. Andrew enlist his brother Simeon (Peter). Jesus then finds Philip who in turn enlist his best friend, Nathaniel. Nathaniel's encounter wit Jesus leads to this first confession of a disciple to Jesus identity as the Son of God, the King of Israel. What is he confessing? What lead to this confession?