The thought process behind Zeras's actions was quite simple.
He knew well that the heavenly punishment to punish him needed to create an avatar of itself.
That avatar would be the one to which the heavenly punishment could sense its power, like water to a bucket.
Judging by the amount of lightning energy present in the sky, Zeras knew that even if he could defeat the lightning, he would still ultimately lose because the avatar would keep getting inexhaustible energy from the heavens, and he would quickly run out.
So he had devised a plan to quickly take the avatar by surprise, crush it beneath his feet, and before it could regain full energy from the sea of tribulation lightning, he would forcefully absorb the avatar into himself.
Almost like swallowing the bucket so that any water that got poured into the avatar would come to him instead.
