Jesus was not denying the legitimacy of biblical law. On the contrary, He was affirming biblical law. We love God first; God commands us to keep His word; therefore, we must enforce the law on ourselves. ↗
The fact is that love is of two kinds, one which commands, and one which obeys. The two are quite distinct, and the passion to which the one gives rise is not the passion of the other. ↗
The czar was always sending us commands - you shall not do this and you shall not do that - till there was very little left that we might do, except pay tribute and die. ↗