Your example isn't a threat because there is no external/conscious actor who is going to cause your body to grow weak and sick if you don't take care of it; it will just happen as a consequence of normal biological processes.
There need not be a consequence of failing to follow the Christian Bible; God/Satan have decided that there will be consequences, and Satan will be the one torturing you if you don't do what God says. That's definitely a threat. In these stories, God and Satan are conscious, sentient beings with free will. They can choose to reward or punish you based on whatever criteria they've decided.
‘I don’t understand something therefore there is no God’ is one of the most common trains of thought that lead to atheism.
Especially and most commonly ‘How could a loving God allow x.’
There isn’t an easy answer to this stuff and I wouldn’t expect there to be. The notion that the universe is easily comprehensible is a framework of thinking that only gets there by discarding everything NOT easily comprehensible and calling the remainder ‘real.’
When people ask why a loving god would allow bad things to happen I want to reply ‘how would you do it better? Design a universe that has meaningful goodness without suffering and evil. Explain how it would work …’
That you favor religion as a resource means your walk is orthogonal to any issues of faith I have. My call to serve as a pastor was hard to justify when I saw suffering. The utility of my faith just isn't a part of the calculus.
There need not be a consequence of failing to follow the Christian Bible; God/Satan have decided that there will be consequences, and Satan will be the one torturing you if you don't do what God says. That's definitely a threat. In these stories, God and Satan are conscious, sentient beings with free will. They can choose to reward or punish you based on whatever criteria they've decided.