1 Timothy 1:5

Here the apostle instructs Timothy how to guard against the judaizing teachers, or others who mingled fables and endless genealogies with the gospel. He shows the use of the law, and the glory of the gospel. I. He shows the end and uses of the law: it is intended to promote love, for love is the fulfilling of the law, Rom 13:10. 1. The end of the commandment is charity, or love, Rom 13:8. The main scope and drift of the divine law are to engage us to the love of God and one another; and whatever tends to weaken either our love to God or love to the brethren tends to defeat the end of the commandment: and surely the gospel, which obliges us to love our enemies, to do good to those who hate us (Mat 5:44) does not design to lay aside or supersede a commandment the end whereof is love; so far from it that, on the other hand, we are told that though we had all advantages and wanted charity, we are but as sounding brass and a tinkling cymbal, Co1 13:1. By this shall all men know that you are my disciples, if you love one another, Joh 13:35.

— Matthew Henry's Concise Commentary (public domain)

But--in contrast to the doctrine of the false teachers. the end--the aim. the commandment--Greek, "of the charge" which you ought to urge on your flock. Referring to the same Greek word as in Ti1 1:3, Ti1 1:18; here, however, in a larger sense, as including the Gospel "dispensation of God" (see on Ti1 1:4; Ti1 1:11), which was the sum and substance of the "charge" committed to Timothy wherewith he should "charge" his flock. charity--LOVE; the sum and end of the law and of the Gospel alike, and that wherein the Gospel is the fulfilment of the spirit of the law in its every essential jot and tittle (Rom 13:10). The foundation is faith (Ti1 1:4), the "end" is love (Ti1 1:14; Tit 3:15). out of--springing as from a fountain. pure heart--a heart purified by faith (Act 15:9; Ti2 2:22; Tit 1:15). good conscience--a conscience cleared from guilt by the effect of sound faith in Christ (Ti1 1:19; Ti1 3:9; Ti2 1:3; Pe1 3:21). Contrast Ti1 4:2; Tit 1:15; compare Act 23:1. John uses "heart," where Paul would use "conscience." In Paul the understanding is the seat of conscience; the heart is the seat of love [BENGEL]. A good conscience is joined with sound faith; a bad conscience with unsoundness in the faith (compare Heb 9:14). faith unfeigned--not a hypocritical, dead, and unfruitful faith, but faith working by love (Gal 5:6).

— Jamieson-Fausset-Brown Commentary (public domain)