'According to the Law' in the Bible

Now some that came down from Judea, taught the brethren, saying, Except ye be circumcised according to the law of Moses, ye cannot be saved.

and join in their expences, that they may shave their head: and that all may know, that there is nothing in what they have heard of thee; but thou thyself walkest according to the law.

Then said Paul to him, "God will smite thee, thou whited wall: dost thou sit to judge me according to the law, and contrary to the law commandest me to be smitten?"