John Gill Commentary John 1:50

"Jesus answered and said unto him, Because I said unto thee, I saw thee underneath the fig tree, believest thou? thou shalt see greater things than these." — John 1:50 (ASV)

Jesus answered and said unto him
Not as reproving him for his faith, as if he was too credulous, and too easily gave into the belief of Christ, as the Son of God, and true Messiah, upon these single expressions of his; but as approving of it, and surprised at it:

because I said unto thee, I saw thee under the fig tree, believest
thou ?
some read the words, not by way of interrogation, but as an assertion; "you believe", or "have believed", as the Vulgate Latin, Arabic, and Persic versions:

you shall see greater things than these ;
meaning that he should have larger discoveries of his person, nature, and perfections, and should see things done by him, much more surprising than any thing he had seen yet; referring to the miracles of raising the dead, casting out devils, and healing all manner of diseases.