But here arises a new question, how can it be that he who has once made such a progress should afterwards fall away? For God, it may be said, calls none effectually but the elect, and Paul testifies that they are really his sons who are led by his Spirit, (Romans 8:14) and he teaches us, that it is a sure pledge of adoption when Christ makes us partakers of his Spirit. The elect are also beyond the danger of finally falling away; for the Father who gave them to be preserved by Christ his Son is greater than all, and Christ promises to watch over them all so that none may perish. To all this I answer, That God indeed favors none but the elect alone with the Spirit of regeneration, and that by this they are distinguished from the reprobate; for they are renewed after his image and receive the earnest of the Spirit in hope of the future inheritance, and by the same Spirit the Gospel is sealed in their hearts. But I cannot admit that all this is any reason why he should not grant the reprobate also some taste of his grace, why he should not irradiate their minds with some sparks of his light, why he should not give them some perception of his goodness, and in some sort engrave his word on their hearts. Otherwise, where would be the temporal faith mentioned by Mark 4:17? There is therefore some knowledge even in the reprobate, which afterwards vanishes away, either because it did not strike roots sufficiently deep, or because it withers, being choked up.
—John Calvin, Commentary on Hebrews 6:4