John 3:8

The wind bloweth - Though the manner in which this new birth is effected by the Divine Spirit, be incomprehensible to us, yet we must not, on this ground, suppose it to be impossible. The wind blows in a variety of directions - we hear its sound, perceive its operation in the motion of the trees, etc., and feel it on ourselves - but we cannot discern the air itself; we only know that it exists by the effects which it produces: so is every one who is born of the Spirit: the effects are as discernible and as sensible as those of the wind; but itself we cannot see. But he who is born of God knows that he is thus born: the Spirit itself, the grand agent in this new birth, beareth witness with his spirit, that he is born of God, Romans 8:16 ; for, he that believeth hath the witness in himself, 1 John 4:13 ; 1 John 5:10 ; Galatians 4:6 . And so does this Spirit work in and by him that others, though they see not the principle, can easily discern the change produced; for whatsoever is born of God overcometh the world, 1 John 5:4 .