Jesus kept the whole law perfectly and so was qualified to be the lamb who would take away the sins of the world.

Christians keep the law by virtue of the keeper being in them and they in Him. We are the righteousness of God InChrist Jesus.

This means that we keep the law by virtue of His HolySpirit in us and us in His HolySpirit.

Because of our NewSpirit (which is integrated with the HolySpirit) we have the law written in our hearts. -> We do not strive to keep it. -> We keep it willingly and supernaturally.