John 5:17 — But Jesus answered them, My Father worketh hitherto, and I work.
18 — Therefore the Jews sought the more to kill Him, because He not only had broken the sabbath, but said also that God was His Father, making Himself equal with God.
God rested on the seventh day because His work of creation was finished. It was good. But when man sinned, God's work of redemption began.
The Father has been unfolding His plan for redemption, and now the Son had arrived to do His role.
hitherto (v. 17) = until now
Jesus Christ is in fellowship with God and shares His council and His work. He is equal with God and therefore God.
He said "My Father," not "our Father." He had a relationship with God they couldn't have. The Jews understood what His words conveyed, although they disagreed.
When the elders said Jesus made Himself equal with God, He didn't disagree with their statement but continued His claims to be God.
The Gospels record seven times when Jesus healed on the Sabbath — Mark 1:21-28; Mark 1:29-31; Mark 3:1-6; Luke 13:10-17; Luke 14:1-6; John 5:1-18; John 9:1-16.