So, although we do have free will, it is still true that God gives us grace that enables us to accept His offer of justification. Moreover, through the sacramental economy, He gives us grace that allows us to perform supernatural acts of virtue.
Our acceptance of His grace is ours; the ability to accept it is freely given by God. It’s a delicate interplay between “grace” and “free choice”, in such a way that we can’t take credit for it, but we nevertheless must make a choice ourselves.
Without that element of “free choice”, the whole system devolves into an exercise in God pulling the strings and forcing us to accept Him.