The phrase ‘union with God’ is paradoxical at first, but becomes clearer when we investigate it.
Let’s take another example: the union of opposites. What does it mean? It means that the one cannot exist without the other.
It means that ying and yan goes together.
Or that females only comes about because there are males, and vice versa.
Now you see what union with God means. It means that the one could not exist without the other. They are related. You are related to God, and cannot exist without Him.