Economy Of Stealing.

Getting here is not the problem. Leaving is the problem. He is currently unnoticed. But that will change if he tries to take anything from the soul spring. While he can sneak past actual barriers without interacting with them and tripping their alarms, he can't take soul stones without interacting with the world. That means the waters of the lake will ripple. 

The rippling of the lake will definitely be noticed. There are a lot of Origin gods with their divine sense and their eyes focused on the lake currently. They will know that someone has snuck in once he makes his move. 

This won't change even if they use illusion to deceive their perception. It is because while they might succeed in hiding the fact that the lake has been touched, they won't be able to hide the fact they have used illusion.