Emphatic, “It was not he who was the light.” Compare Joh 2:21, “He (ἐκεῖνος) spake,” bringing out the difference between Jesus' conception of destroying and rebuilding the temple, and that of his hearers.
That light (τὸ φῶς)
Rev., the light. The emphatic that of the A.V. is unnecessary.
Was sent
Rev., came. Neither in the original text. Literally, “He was not the light, but in order that (ἵνα) he might bear witness.” So in Joh 9:3. “Neither hath this man sinned, nor his parents, but (he was born blind) that the works,” etc. Compare Joh 15:25.