William Burkitt on John 16:25

Here our Saviour tells his disciples that although he had spoken many things to them in dark parables and figurative expressions, yet now the time was approaching, namely, the Comforter's coming, when he would, by the Holy Ghost, clearly enlighten their understandings in the knowledge of divine mysteries, and the things pertaining to the kingdom of God, and particularly in the knowledge of God as his Father, and their Father in him.

Hence learn, 1. That the clearest truths will be but parables, proverbs, and dark myteries, even to disciples themselves, till the Holy Spirit enlightens their understandings.

2. That the clear and full manifestation of divine truth was reserved till the coming of the comforter, who did communicate it to the apostles, and by them to the church, or body of Christians: I, by him, will shew you plainly of the Father.