'Instructions' in the Bible

So then, brethren, stand firm, and hold fast the instructions which ye have been taught, whether by word or by our letter.

Now we command you, believers, in the name of our Lord Jesus Christ and by His authority, that you withdraw and keep away from every brother or sister who leads an undisciplined life and does not live in accordance with the tradition and teaching that you have received from us.

and if any one refuses to obey these our written instructions, mark that man and hold no communication with him--so that he may be made to feel ashamed.