When the jewish leaders first brought Jesus to the Roman authorities to crucify Him, they refused to state a charge. They just said “we wouldn’t have brought Him here is He wasn’t worthy of death.” When it became clear that Pilate wanted to let Jesus go, they finally came back with a charge. You can read it in John 19:7:
John 19:7 - KJV
7. The Jews answered him, We have a law, and by our law he ought to die, because he made himself the Son of God.
That’s it. That’s the charge. He made himself the son of God. The only thing they could find to crucify Christ for was that He claimed to be the son of God.
Jesus, for his part, was both guilty and innocent of that charge. He was guilty, of course, because he was the son of God. He did claim, on many occasions to be God. For instance, He said clearly:
John 8:58 - KJV
58. Jesus said unto them, Verily, verily, I say unto you, Before Abraham was, I am.
Jesus claimed to be around before Abraham and used God’s name “I am that I am.”
He also said, in John 10:30
John 10:30 - KJV
30. I and my Father are one.
So Jesus was absolutely guilty of claiming to be the son of God. He actually went further than that and claimed to be God.
But He was also innocent, because he didn’t “Make himself the son of God” like He was play acting. Like He was some kind of con man trying to pass himself off as someone He was not.
No, Jesus was God the Son. Coequal with God the Father. John 1:1, speaking of Jesus says:
John 1:1 - KJV
In the beginning was the Word, and the Word was with God, and the Word was God.
But why was it necessary for God to send His son to die for us on the cross? Let me give you two reasons:
First, our substitute had to be a man. We don’t accept the substitute of a different kind. No society would let a man’s dog serve jail time for him. We wouldn’t accept a goldfish as a substitute for a man in a capital punishment case. Whoever took our place on the cross had to be a man so he could take the place of men.
And Jesus really came, born as a man, with real human flesh and blood. He was 100% man.
But Jesus also had to be God. Because a man could only be the substitute for one man. But God, punished in our place, could be the substitute for all men.
So Jesus came as the God-man. 100% man, 100% God. He died in our place as our worthy substitute - and God’s justice was satisfied. His death will count for you too, if you accept Him by faith.
So Jesus died on the cross because He made Himself the son of God. And we are glad He did, because that is why He could save us.