Burkitt:

MY little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous: 2 And he is the propitiation for our sins; and not for ours only, but also for the sins of the whole world.

Observe here. The compellation. First, My little children. The apostle calls the Christians lo whom he wrote. Children, little children; his little children. He calls them Children, because converted to Christianity; little children, because young and lender Christians, of a low stature in religion, and far short of manly perfections; and his little children, to denote that spiritual relation which was between him and them, and that endeared affection which he bare towards them. St. John, by a loving compellation, makes way for a faithful admonition, which follows in the next words: These things I "write, that ye sin not. This must be understood in a qualified sense, thus: 1. Sin not, that is, as the wicked sin; take heed of scandalous enormities, though you cannot shake off daily infirmities. 2. Sin not, as in the same kind that others sin, so neither in the same manner that you yourselves before sinned; sin not with that fullness of deliberation, with that freedom of consent, sin not with that strength of resolution, with that frequency of action, with which you sinned before you were called to Christianity. 3. Sin not: that is, as fur as human nature will admit, abstain from all sin; let it be your care, prayer, study, endeavor, to keep yourselves from every evil thing. Thus Zachary and Elisabeth were blameless, Luke i. 6, that is, they lived in no sin known to the world, or known to themselves; so it is said of Job, ch. i. alt. he sinned not, that is, had no sin prevailing in him; no sin indulged by him. Observe, 3. As the cautionary direction, sin not: so the comfortable conclusion, but if any man sin, that is, through infirmity and weakness, through the policy of the tempter, or by the surprise of a temptation, we have an advocate, a mediator, and an intercessor in heaven, who is absolutely sinless, even Jesus Christ the righteous. It is a metaphor taken from courts of judicature, where are the guilty person, the accuser, the judge, and the advocate: thus here heaven is the court, man is the guilty person, Satan the accuser, God the judge, Christ the advocate. The proper office of an advocate is, not to deny the fact, or disown the guilt, but to offer something to the judge, whereby the law may be satisfied, and upon which the judge may, without any unrighteousness, discharge the accused. Observe, 4. An invaluable privilege here discovered, that Christ our advocate became a propitiation for us, and for the whole race of mankind, for all that lived before us, or shall live alter us, for Jews and Gentiles: there is a virtual sufficiency in the death of Christ for all persons, and an actual efficacy as to all believers. Learn hence, That our Lord Jesus Christ, suffering death upon the cross for our redemption, did by that one oblation of himself once offered, make a full, perfect, and sufficient sacrifice, oblation and satisfaction, for the sins of the whole world. The original word propitiation, signifies a propitiatory covering, an allusion to the mercy-seat that covered (he ark, in which the law was. In allusion to which, Christ is here called our propitiatory covering, because he hides our sins, the transgressions of the law, from his Father’s sight.

William Burkitt, Expository Notes With Practical Observations on the New Testament (Philadelphia: Published by Thomas Wardle, 1835), 2:767-758. [Italics original; underlining mine.]