This is hardly the place to discuss General Relativity but I can give a small explanation. Do you know the metaphor for gravity with a rubber sheet? Masses make

This is hardly the place to discuss General Relativity but I can give a small explanation. Do you know the metaphor for gravity with a rubber sheet? Masses make dimples in the sheet and when particles pass, they get deflected. Similarly, when something moves past the Sun, it gets deflected and that's the reason we stay in orbit. Of course you could say you're holding your arm still and there's no reason for it to veer of course and suddenly start moving. But it actually is in motion, everything moves through time! It's this movement that gets deflected into spatial directions. We human observers have to move through time, we can't stop to get the big picture and that's why objects in the vicinity of masses suddenly start accelerating. ...Maybe I should write a book.