Setting your life total to a higher number counts as gaining life. So if you're unable to gain life, there's no way for your life total to increase.
So your opponent is staring you down with an active , or maybe his is online and giving you the business. Your board is fairly barren, but you've got a nice little in your hand, and you're ready to turn that threat into an answer! Well, you shouldn't. Devotion is a static ability on the five Gods we have, and it's constantly checking itself. If you take over their god with your or , the chances are low that you'll get to keep it! As soon as the God switches over to your control, it'll check
We delve into a tricky rules interaction with gods entering the battlefield while devotion to their color is exactly 4 before they enter.