Mark 12:35-44

I'm very confused by the first part of this passage. Not exactly sure what I should be getting from it. Did people think David was THE son of God? I see in the second part of this scripture the value of a purity and honestly of heart. Prayer should be sincere, not lengthy for time's sake. And money tithed should be given with trust in the Lord, pushing ourselves to lean on Him. I need to do this more. I've been afraid to lean.