Gerhard argues powerfully against a Stoic determinism when it comes to the time and manner of one’s death (On Death, § 61). Most Christians are not tempted to an Epicurean view that their days are mere chance and their death random. They know it is in God’s hands. They are tempted, however, to think that it matters not how they live since God already knows when our time will come. He does know, but He knows in view of the choices we make and the actions we will take. The Bible is clear that those who lead a godly life should expect length of days (Deut. 6:2; Eph. 6:3; Prov. 3:2, 16; 1 Peter 3:10; the examples of Nineveh, Hezekiah, Uzziah, and a thousand other passages and histories). The godly should expect a long life ordinarily, and if this does not happen it is because God’s is giving us better, heavenly goods and sparing us the miseries and temptations to loss of faith which are ever present in this life. On the other hand, the ungodly and wicked should expect a worse life and quicker end. That there are exceptions to this proves the rule.
If this were not the case several absurdities would follow (ibid. 66.VI):
If both the hour and the kind of death have been determined by some absolute and fated necessity: (1) Vain will be the divine promises about the long life to be expected by the godly. (2) Vain will be the divine threats with which God threatens the ungodly with a shortening of life and a tragic death. (3) Vain will be the prayers of the godly in which they ask long life and a peaceful death for themselves and for others. (4) Vain will be the use of medicine. (5) Those who inflict violent hands upon themselves will be bound [to commit] this sinful act by an absolute decree of God. (6) Those who because of their disgraceful acts die a violent and shameful death by the sword, the rack, the rope, etc., and are carried off to punishment would perish with this kind of death by an absolute decree of God and a sort of Stoic fate. In fact, God would be made the instigator of those sins.
Two common errors present themselves. The first is when people try to pry into the secret things of God and discern from events the manner and quality of someone’s life. We know God’s love and favor not from our circumstances but from the cross of Christ. In other words, one cannot assume that because a man died young that he was ungodly. For example, the martydrom of the holy innocents and their early deaths does not imply anything to us about their eternal salvation. The second error is to assume that this scriptural teaching is a form of works-righteousness. But this teaching is not addressing how one becomes righteous before God (by faith in Christ alone) but how those who are righteous before God live and what manner of life they generally have (a comparitavely good one). It is not works-righteousness to believe the promises of God clearly stated in Scripture in which the godly are told, generally speaking, to expect long life and good days for walking in the wisdom and ways of God.
Many people in our worldly-minded culture want to preserve and prolong their life. They try to do this through diet, exercise, and such. These things ought not be neglected or denied by Christians. We should not be gluttonous but live in the fruit of the Spirit called self-control. But if people really wanted to live a long and good life, they would walk with God in humility and faith. To be sure, bodily fitness and spiritual fitness or not opposites. But one is far greater than the other. The wisdom of God is greater than the wisdom of fitness experts. As St. Paul summarizes: Train yourself for godliness; for while bodily training is of some value, godliness is of value in every way, as it holds promise for the present life and also for the life to come (1 Tim. 4:7-8).