Grace as a weapon

Grace is one of the most valuable gifts given in Christianity next to forgiveness. However, the world has a tendency to weaponize “grace” against Christians, Even more confusing, Christians weaponize “grace” against other Christians. How does having grace, or not having grace, factor into the perception of believers and non-believers? Do non-believers get grace from God? How about in the old Testament before Christ was birthed and died for our redemption, where was grace?