The causa prima (i.e. first cause), and impulsive cause, [of our salvation] was free grace. It was love in God the Father to send Christ, and love in Christ that He came to be incarnate.
Love was the intrinsic motive.
Christ is God-man, because He is a lover of man. Christ came out of pity and indulgence to us: non merita nostra, sed misera nostra (Augustine)–‘Not our deserts, but our misery’ made Christ take flesh. Christ’s taking flesh was a plot of free grace, and a pure design of love.
God Himself, though Almighty, was overcome with love. Christ incarnate is nothing but love covered with flesh. As Christ’s assuming our human nature was a master-piece of wisdom, so it was a monument of free grace.