When God encourages us with warnings and exhortations at the same time He stirs up our hearts so that the exhortations are not in vain and do not pass away without effect. Therefore we cannot gather from precepts and exhortations the power a man has of himself or the capacity of his free will, for the attention which the apostle here requires [Hebrews 12:15] is the gift of God.
-- John Calvin, Calvin's New Testament Commentaries: Hebrews and I & II Peter, translated by William B. Johnston, page 196