Regarding all this “why bother” stuff:
Predestination is a small part of Calvinist theology and one of the most misunderstood ideas in history: it is a logical consequence of God’s omniscience, that’s all. Since God knows everything, he must know who is going to be saved and who damned; since he is omnipotent, he must have chosen those people. But that doesn’t mean that everything is irrelevant, since Calvinism doesn’t assume a totally absent, passive God who picks people for salvation and then watches the world run. In fact, it’s quite the opposite: God is completely and totally active, and will strike down anyone who mocks him quickly and without any mercy. Acts of providence, on the other hand, are signs of God’s approval and support for those waging a war against the ungodly (in practice, this was interpreted as Catholics, Muslims, and Jews, for the most part).
The most important part of Calvinism is that absolutely everything is a consequence of God’s will. Random accidents - you slip and stub your toe, you find five bucks - are signs from God. Calvinists didn’t pretend to understand all of God’s actions, of course. And obviously sometimes good things happen to bad people. This was merely due “to God’s free love and grace that will show mercy to whom he will show mercy,” as Nehemiah Wallington said. And sometimes bad things happen to good people, but this is just a consequence of the assumed fact that all people are sinners - no one is believed to be basically good.
In addition, both of these problems - that the unholy are sometimes blessed, and the holy are punished - were also sometimes hailed as signs of the coming of the Antichrist which was, somewhat counterintuitively, viewed as a good thing. The coming of the Antichrist would signal the return of the Messiah in a huge war of believers versus sinning followers of the Antichrist. The godly would inevitably win this war and be rewarded with eternal salvation, so many Calvinists looked forward to that battle, or viewed daily events as small battles in the broader war that they believed was already going on (at various times various Calvinists accused the Pope of being the Antichrist).
This idea of divine influence in all things also provided a comforting level of stability and order to things, even if people can’t understand it. It’s a way of completely ceding control of things to God, which can make people feel more secure and give them a way of making sense of the chaos of the world - or if not make sense of it, at least believe that there is an underlying system, not random actions.
It also lends comfort in promising the inevitability of a victory for believers. This is easily seen in Puritan texts and sermons in the years leading up to the English Civil War. Nehemiah Wallington again: “The wicked always hate the godly and plot against them,” so “you may see now how Antichrist, even these bloody-hearted papists, doth plot against the poor Church of God, as in '88 and that hellish Gunpowder Plot. And how have they laid snares for the poor children of God, as with the cursed Book of Canons with that execrable oath… But He that sits in heaven laughs them to scorn and hath brought all their devices to naught.”
Once Calvinism started spreading, social factors kept it alive. In practice, Calvinist culture was extremely religious, since those who aren’t members of the elect (ie, people who won’t be saved) are shunned by the religious community. So, to stay within the society, people want to prove that they are part of the elect by living extremely religious lives. By merely saying “it doesn’t matter what I do,” you are indicating a lack of religiosity and an apathy towards God. Calvinism emphasizes praising God for his mercies as well as his punishments, not because of a belief that this will lead to salvation but because it should show that you are living a saintly life, and therefore a member of the elect.
People who didn’t follow a godly life were quickly shunned by the entire community. Think Hester Prynne in The Scarlet Letter: she’s seen as a sinner, and so she is completely exiled. Even being seen with her is a scandal.
Edit: I’d hasten to add that I am** not** a Calvinist, I merely study the period in European history.