... The thing I never understood about Christianity is why Christ had to die for sins to be forgiven. ......
Well, at the risk of dragging the thread even further off topic, this is a really primary question. If I could rephrase your question, you have essentially asked "The thing I never understood about Christianity is Christianity."
I am frankly a little surprised that more folks in contemporary society do not ask this question. It made a lot of sense to first century Jews, but it does not really make sense to a lot of 21st century peoples.
In the Old Testament, God established that people need to make atonement for sin. The establishment of the atonemment mechanism started early (with the first shreds in the Cain/Abel story in Genesis) and with full description in the Mosaic law (in Leviticus). The model was that people offered sacrifices of animals throughout the year, and a major sacrifice at a particularly holy sacrificial ceremony on the annual day of atonement (this is the present day Yom Kippur).
To us 21st century folks, this seems sort of barbarian, and I don't claim to understand why God established this particular mechanism. As you suggested, He could do whatever he wanted. Nevertheless, God established that the penalty for doing things wrong (sin) is death, and that the death of an animal offered in humility would temporarily atone for the wrongs committed by His people.
Christ came along to act as the final "sacrificial lamb" for all generations. That is, Christ's death was required, and Christ also had to be sinless. The critical element is that the "highest righteousness of man" is not good enough for God, so He established a mechanism to make us holy by His own power.
If you take Christ's death out of Christianity, there is no Christianity left.
If you want to talk more about this, you ought to start a new thread. This one was started to talk about apparent contradictions in the Bible.