Make some sense

I haven’t gotten to the New Testament yet, but I have a rough understanding of what Christianity means.  I was raised nominally Lutheran, but my parents are, I suspect, deists.

So, here is what does not make sense to me, and correct me if I am wrong:

God sacrificed himself, to himself, to forgive the sins that were a violation of the rules he made up, that fallible, mortal creatures he made mortal and fallible, made?

 For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life. John 3:16

That makes no fucking sense, but, as far as I can tell, is what Christianity is all about.  Why can’t god just forgive?  Why does it need worship and belief?  God makes the rules, why can’t it change them?  Why did it not make us perfect and eternal in the first place?  It shows regret in the Bible:

And the LORD repented that He had made man on the earth, and He was angry to His heart. And the LORD said, I will destroy man whom I have created, from the face of the earth, both man, and beast, and the creeping thing, and the fowls of the air. For I repent that I have made them. Genesis 6:4

For that matter, why is the LORD a he?  A god would not need a gender.  It is part of sexual reproduction.  God does not need to have sex or reproduce.  How can it have a son?  How can it mate with a human?  None of this makes sense, and the more you think about it, the worse it gets.