People will sometimes caricature Calvin’s doctrine of predestination by saying “Well, if everything is predestined then it doesn’t matter what we do…because it was predestined.”.
This, of course is a careless way to understand the bible’s teaching and Calvin’s explanation thereof.
The Westminster Confession rightly affirms the biblical doctrine of predestination and offers an excellent pastoral warning-
The doctrine of this high mystery of predestination is to be handled with special prudence and care, that men, attending the will of God revealed in His Word, and yielding obedience thereunto, may, from the certainty of their effectual vocation, be assured of their eternal election. So shall this doctrine afford matter of praise, reverence, and admiration of God; and of humility, diligence, and abundant consolation to all that sincerely obey the Gospel. (WCF 3.8)
To understand Calvin’s practical outlook on predestination, his comments on Isaiah 6 and John 12 are helpful. These passages have to do with God hardening the hearts of the Jews so they would not respond to the gospel. Who’s fault is their unbelief? See Calvin’s comments connected to these passages:
Though he (Jesus) had done so many signs before them, they still did not believe in him, so that the word spoken by the prophet Isaiah might be fulfilled:
“Lord, who has believed what he heard from us, and to whom has the arm of the Lord been revealed?”
Therefore they could not believe. For again Isaiah said,
“He has blinded their eyes
and hardened their heart,
lest they see with their eyes,
and understand with their heart, and turn,
and I would heal them.” John 12:36b-40
John quotes Isaiah 6 as a clear demonstration of the stubbornness of the Jews. He does not indeed absolutely give the very words, but he states the meaning clearly enough.
Therefore, says he, they could not believe, because Isaiah said, He hath blinded their eyes, and hardened their heart.
True, this prediction was not the cause of their unbelief, but the Lord foretold it, because he foresaw that they would be such as they are here described. The Evangelist applies to the Gospel what had already taken place under the law, and at the same time shows that the Jews were deprived of reason and understanding, because they were rebels against God. Yet if you inquire into the first cause, we must come to the predestination of God. But as that purpose is hidden from us, we must not too eagerly search into it; for the everlasting scheme of the divine purpose is beyond our reach, but we ought to consider the cause which lies plainly before our eyes, namely, the rebellion by which they rendered themselves unworthy of blessings so numerous and so great. (Calvin's commentary on Isaiah 6)
Did you catch what Calvin said? The ultimate driver behind the actions of men is God’s sovereign hand, however understanding the purpose on the level of predestination is too hard and not clearly revealed to us. For us, practically speaking, we are to see rebellion for what it is- sin. Man is responsible for his sin no matter what the hidden, sovereign plan of God might be accomplishing. In Isaiah 6 and John 12 the Jews were responsible for their disbelief. Unbelievers are responsible for their unbelief.
We can never use predestination to excuse sin and disbelief.