15:1 I am. This is the seventh and last of the “I am” statements of Christ in John’s gospel, all asserting His deity and complete ability to save and reign. The others are, in order: (1) “the bread of life” (John 6:35); (2) “the light of the world” (John 8:12); (3) “the door” (John 10:9); (4) “the good shepherd” (John 10:11); (5) “the resurrection, and the life” (John 11:25); (6) “the way, the truth, and the life” (John 14:6). As the seven “I am’s” affirm His deity, the seven “signs” (see John 20:30-31) confirm it.
15:1 true vine. Israel had been pictured in the Old Testament as a vine that had become unproductive (e.g., Isaiah 5:1-7; Jeremiah 2:21), but Christ here asserts that He Himself is the “true vine,” whose good fruits last forever.
15:2 he taketh away. The true Christian will bear good fruit; the pseudo-Christian will not bear good, lasting fruit, and will therefore ultimately be cast into the fire and burned (John 15:6), just like the pseudo-wheat in the parable of wheat and tares (Matthew 13:28-30,41-42).
15:2 beareth fruit. Note the threefold categories of Christians: (1) fruit-bearing (John 15:2); (2) more fruit-bearing (John 15:2); (3) much fruit-bearing (John 15:5). These seem to correspond to the three categories of wheat-producing Christians—those producing thirtyfold, sixtyfold and hundredfold returns (Matthew 13:8,23).
15:2 purgeth it. The “purging” or “pruning” obviously refers to bringing whatever pressures on the believer may be needed in order to lead him into a more fruitful Christian life and witness.