Matthew Poole and continuators on John 1:31

31 And I knew him not : but that he should be made manifest unto Israel , therefore am I come baptizing with water .

This verse is best expounded by v. 33. where the same words are repeated, I knew him not; and is added, but he that sent me to baptize with water, the same said unto me, Vpon whom thou shalt see the spirit descending, &c. Lest any should think that Christ and Iohn had compacted together to give one another credit, or that there was some near relation betwixt Iohn and Christ, Iohn saith, I knew him not, for Christ had spent his time at home, Luk. 2.51. Iohn had lived in desert places, the Providence of God so ordering it, that Iohn should not know Christ, so much as by face, until that time came, when Christ was to be made manifest to Israel.

But that God might make his Son manifest unto Israel, when God by an extraordinary mission sent Iohn to Baptize with Water, he gave him this token, That he upon whom he should see the Spirit descending and remaining on him, as v. 33. that was the Messiah, the Lamb of God, that should take away the Sin of the World; he who should baptize with the holy ghost.

And therefore (saith Iohn) I came baptizing with water. I did not run without sending, nor introduce a new rite or Sacrament without Commission; but being thus sent of God, and that I might give Christ an opportunity of coming to me, that I might see the Spirit descending and remaining upon him. From whence we learn, That none but Christ can institute a Sacrament. Iohn Baptized not, till he was sent to Baptize with Water.