John 1:37

We have here the turning over of two disciples from John to Jesus, and one of them fetching in a third, and these are the first-fruits of Christ's disciples; see how small the church was in its beginnings, and what the dawning of the day of its great things was. I. Andrew and another with him were the two that John Baptist had directed to Christ, Joh 1:37. Who the other was we are not told; some think that it was Thomas, comparing Joh 21:2; others that it was John himself, the penman of this gospel, whose manner it is industriously to conceal his name, Joh 13:23, and Joh 20:3. 1. Here is their readiness to go over to Christ: They heard John speak of Christ as the Lamb of God, and they followed Jesus. Probably they had heard John say the same thing the day before, and then it had not the effect upon them which now it had; see the benefit of repetition, and of private personal converse. They heard him speak of Christ as the Lamb of God, that takes away the sin of the world, and this made them follow him. The strongest and most prevailing argument with a sensible awakened soul to follow Christ is that it is he, and he only, that takes away sin. 2. The kind notice Christ took of them, Joh 1:38.

— Matthew Henry's Concise Commentary (public domain)