That’s what one elderly lady asked me. She’s also catholic, but maybe not quite strong enough in it. I tried to explain it but it was quite difficult. I told her God was, is and always will be and that’s why Jesus said to his disciples when you see me you’ve seen the Father. Then I explained that the FATHER wanted a human to be born that would take on the sins of the world in crucifixion, so that’s why Mary was created and without sin yet. She did the Lords will without question. And of course after Jesus died and arose from the dead He was truly the Holy Spirit. You know the devil said no man could go through what the Lord went through in the crucifixion, but the devil was so wrong, as he always is. After all, Jesus wasn’t just human, he was divine in nature. Can you add any more to that? Or am I way off base? Maybe you have a better answer. Just E-Mail the answer to me at email@example.com. Thank you and GOD BLESS YOU ALL.
Her confusion may be in thinking that man took on being God when it was just the other way around: God took on being man, and he can do anything he likes for whatever reasons seem good to him.
Good questions to ask when wondering about such things are:
Could God do it?
Being a God of justice, mercy, and love, would God do it?
I find these questions usually sort things out these sorts of questions about what God did or why did God do this or that.