John Lightfoot on John 15:1

[I am the true vine.] We may take these words in opposition to what is spoken concerning Israel. Israel is called a vine, Psalm 80:8; Isaiah 5:7; Jeremiah 2:21, &c. In Vajicra Rabba, the parallel is drawn between Israel and a vine; and the similitude is carried on to sixteen particulars, for the most part improper and unsuitable enough.

But that which is principally to be regarded in this place is this, that hitherto, indeed, Israel had been the vine, into which every one that would betake himself to the worship of the true God was to be set and grafted in. But from henceforward they were to be planted no more into the Jewish religion, but into the profession of Christ. To which that in Acts 11:26 hath some reference, where the disciples were first called 'Christians,' that is, no longer Jews or Israelites.

Our Saviour, as we have said before, discoursed these things immediately after that he had instituted the holy eucharist: while he was ordaining that holy sacrament he had said, "This is the new testament in my blood"; and from thence immediately adds, I am the true vine: so that for the future the church is to be under the administration of a new testament, and not, as the Jewish church, under that of the old; and from henceforward I am the true vine, into which all the branches of the church must be ingrafted, and not into the Israelitish vine any more.