Charles H. Spurgeon on Psalms 141:3

Set a watch, O Lord, before my mouth, etc. Thus holy men have kept the sessions at home, and made their hearts the foremen of the jury, and examined themselves as we examine others. The fear of the Lord stood at the door of their souls, to examine every thought before it went in, and at the door of their lips, to examine every word before it went out, whereby they escaped a thousand sins which we commit, as though we had no other work. —Henry Smith.