A.T. Robertson 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)

Answered and said (απεκριθη κα ειπεν). This redundant use of both verbs (cf. 1:26) occurs in the Synoptics also and in the LXX also. It is Aramaic also and vernacular. It is not proof of an Aramaic original as Burney argues (Aramaic Origin, etc., p. 53).

Because (οτ). Causal use of οτ at beginning of the sentence as in 14:19; 15:19; 16:6. The second οτ before ειδον (I saw) is either declarative (that) or merely recitative (either makes sense here).

Thou shalt see greater things than these (μειζω τουτων οψη). Perhaps volitive future middle indicative of οραω (though merely futuristic is possible as with οψεσθε in 51) ablative case of τουτων after the comparative adjective μειζω. The wonder of Nathanael no doubt grew as Jesus went on.