Fisher's Catechism, Q.14:
Q. 15. How are actual sins divided?
A. Into sins of omission and commission.
Q. 16. What is a sin of omission?
A. It is a neglecting, or forgetting to do that good which the law commands, James 4:17.
Q. 17. What is a sin of commission?
A. It is a doing of what the law of God forbids, Psalm 51:4.
John Brown of Haddington's exposition of the Westminster Shorter Catechism:
Q. How may actual sin be distinguished? -- A. Into sins of omission and of commission.
Q. What understand you by a sin of omission? -- A. Our neglecting to perform that which God's law requires.
Q. What mean you by a sin of commission? -- A. Our doing that which God's law forbids, Hos. iv.2.
How humbling is it to realize that not only do we actively sin against God's perfect and law, but we also transgress by evading our duties. Who can keep the fullness of God's requirements to not only abstain from this or that, but to do all that we are supposed to do? We are all unprofitable servants. This must have been on the mind of James Ussher as he breathed his last. Ussher's last words on his deathbed on March 21, 1656 are reported to be: "O Lord forgive me, especially my sins of omission." The mercy of God, through Jesus Christ -- this is our only hope.
If thou, LORD, shouldest mark iniquities, O Lord, who shall stand?
But there is forgiveness with thee, that thou mayest be feared. (Ps. 130.3-4)
"A General Confession of Sin,” from the Anglican Book of Common Prayer (1552 edition), penned by Thomas Cranmer:
ALMIGHTY and most mercyfull father, we have erred and strayed from thy wayes, lyke lost shepe. We have folowed too much the devises and desyres of oure owne hearts. We have offended against thy holy lawes. We have left undone those things whiche we oughte to have done, and we have done those thinges which we ought not to have done, and there is no health in us: but thou, O Lord, have mercy upon us miserable offendors. Spare thou them, O God, which confesse theyr faultes. Restore thou them that be penitent, according to thy promyses declared. unto mankynde, in Christe Jesu oure Lorde. And graunt, O most merciful father, for his sake, that we may hereafter live a godly, righteous, and sobre life, to the glory of thy holy name. Amen.