The same came for a witness, to bear witness of the Light, that all men through him might believe.
Does the light then need that witness should be borne to it? Is not light its own evidence? Yes, if men have eyes to see; but because they lay in the darkness and slumber of sin, it was necessary to arouse them, and to give testimony to the true light, distinguishing it from all false lights that could only lure to death. In an obvious sense, "the law and the prophets" formed a great system of "witness" to the coming One (Acts 10:43; Romans 3:21, 22); but it required completing, and John's ministry was the completion of it — the grand close of the prophetic symphony. The morning star, day's harbinger, bears witness of the sun, by shining in his light; and so also does the mountain top, kindled with the first rays of morning, to the dwellers in the deep valley beneath, or the far-stretching plain. But John's testimony went beyond even this: he not merely preceded the Messiah, closing the prophetic line, but, having first aroused the nation by that cry, "Repent," he actually introduced and named Him to Israel.
(J. Culross, D. D.)
Parallel VersesKJV: The same came for a witness, to bear witness of the Light, that all men through him might believe.