Desert Fathers

John who had been exiled by the Emperor Marcion, said, 'One day we went into Syria to see Poemen for we wanted to ask him about hardness of heart. But he did not know Greek and we did not have an interpreter. When he saw we were embarrassed, he began to speak in Greek saying, 'The nature of water is soft, the nature of stone is hard; but if a bottle is hung above a stone letting water drip down, it wears away the stone. …

The Desert Fathers, Sayings of the Early Christian Monks ↗

Augustine of Hippo

God by his grace takes away the stony heart from unbelievers and forestalls merit in people of good will in such a way that their will is prepared by what goes before grace, but that grace is not given through some merit of human will.

Letter 217 ↗

Jerome

And it is to be considered that a new heart and a new spirit are given through the effusion and sprinkling of water. When, however, a new heart and a new spirit are given, then all hardness, which is compared to stone, will be removed from the Jewish heart, so that the heart may be a fleshy, soft, and tender one, which can receive the spirit of God within itself and be inscribed with saving words. …

Commentary on Ezekiel ↗