The owner of a vineyard sent slave after slave "to the tenants to obtain from them his share of produce from the vineyard" (Mk 12:2). "Some they beat; some they killed. He still had one to send — the son whom he loved. He sent him to them as a last resort, thinking, 'They will have to respect my son' " (Mk 12:5-6). "Then they seized and killed him and dragged him outside the vineyard" (Mk 12:8). The owner of the vineyard seems astoundingly stupid for continuing to send slaves to almost certain beatings or death and then send his own son to be killed.
In this allegory, the owner of the vineyard represents God the Father. He sent prophet after prophet to turn us away from our sins. Almost all of these prophets were rejected. Many were murdered. Then God the Father sent His Son. Unlike the owner of the vineyard in the allegory, God the Father knew for certain that His Son, Jesus, would be tortured, nailed to a cross, and murdered. Nevertheless, He sent Jesus so that all could be saved from sin and death, and some would be saved.
If you knew a person would be party to killing your child, would you send your child to him? Would you create a person you knew would drive a nail into your child or imbed a thorn into his head? God the Father did this when He created each one of us and sent His Son, Jesus, to save us. Why did He do this? "God is Love" (1 Jn 4:16).