The workings of grace in the heart are utterly mysterious and unsearchable. We cannot explain why the word produces effects on one person in a congregation, and not upon another.
We cannot explain why, in some cases–with every possible advantage, and in spite of every entreaty–people reject the word, and continue dead in trespasses and sins. We cannot explain why in other cases–with every possible difficulty, and with no encouragement–people are born again, and become decided Christians. We cannot define the manner in which the Spirit of God conveys life to a soul, and the exact process by which a believer receives a new nature. All these are hidden things to us. We see certain results, but we can go no further. “The wind blows where it wishes, and you hear its sound, but you do not know where it comes from or where it goes. So it is with everyone who is born of the Spirit.” [John 3:8]
We cannot explain why, in some cases–with every possible advantage, and in spite of every entreaty–people reject the word, and continue dead in trespasses and sins. We cannot explain why in other cases–with every possible difficulty, and with no encouragement–people are born again, and become decided Christians. We cannot define the manner in which the Spirit of God conveys life to a soul, and the exact process by which a believer receives a new nature. All these are hidden things to us. We see certain results, but we can go no further. “The wind blows where it wishes, and you hear its sound, but you do not know where it comes from or where it goes. So it is with everyone who is born of the Spirit.” [John 3:8]
~ J.C. Ryle
Expository Thoughts on the Gospels: Mark, [Carlisle, PA: Banner of Truth, 1985], 74-75. {Mark 4:26-29}