"According to the will of our God and Father" (Galatians 1:4b)
It was God the Father's good will, it pleased him so to give up his only Son to death for our sins. He is God and he does as he pleases.
But it pleased God's Son as well to come and die, because it says, he, Jesus "gave himself for our sins..."! No one forced him or make him to come and die in our place, he did it of his own free will.
And so the will of God, of the Father and the Son is one, they both willed the death of God's unique Son, Jesus Christ.