Nathaniel says Jesus is "the Son of God" because Jesus knew Nathaniel without previously meeting him.
# Son of God
This is an important title for Jesus. (See: [[rc://en/ta/man/translate/guidelines-sonofgodprinciples]])
# Because I said to you ... do you believe?
This remark appears in the form of a question to provide emphasis. AT: "You believe because I said, 'I saw you underneath the fig tree'! (See: [[rc://en/ta/man/translate/figs-rquestion]])
# Truly, truly
Translate this the way your language emphasizes that what follows is important and true.