I Thessalonians 4:3

This is the will of God, even your sanctification - God has called you to holiness; he requires that you should be holy; for without holiness none can see the Lord. This is the general calling, but in it many particulars are included. Some of these he proceeds to mention; and it is very likely that these had been points on which he gave them particular instructions while among them. That ye should abstain from fornication - The word πορνεια, as we have seen in other places, includes all sorts of uncleanness; and it was probably this consideration that induced several MSS., some versions and fathers, to add here πασης, all. Directions of this kind were peculiarly necessary among the Greeks, and indeed heathens in general, who were strongly addicted to such vices.

For--enforcing the assertion that his "commandments" were "by (the authority of) the Lord Jesus" (Th1 4:2). Since "this is the will of God," let it be your will also. fornication--not regarded as a sin at all among the heathen, and so needing the more to be denounced (Act 15:20).

For this is the will of God, even your sanctification,.... Which is another reason to enforce the above exhortation. "Sanctification" is internal or external. Internal sanctification is the work of the Spirit of God, and is a principle of spiritual life in the soul, a divine and spiritual light in the understanding, a flexion of the will to the will of God, and a settlement of the affections on divine things, and is an implantation of every grace in the heart. External sanctification arises from this, and lies in holiness of life and conversation; and is what is chiefly designed, as appears both by what goes before, and follows after: and this is "the will of God"; the will of his purpose and decree; for in the same decree that he wills the salvation of any by Jesus Christ, he also wills their sanctification in heart and life, and here and hereafter: and this is his approving will, or what is well pleasing in his sight, being agreeable to his nature, and divine perfections, particularly his holiness, in which he is glorious; and it is his will of command, and what he requires in his law, which is holy, just, and good, and perfectly agrees with the sound doctrine of the Gospel, and the revelation of his will in both. That ye should abstain from fornication: which is particularly mentioned, abstinence from it being a branch of external holiness; and because that this sin was common among the Gentiles, and not esteemed a sin by them; as also to observe to these Christians, that as simple fornication was not to be allowed of, much less other acts of uncleanness, as adultery, incest, sodomy, and the like, which were iniquities that greatly prevailed among the Heathens. The Syriac version renders it, "from all fornication"; on this subject the apostle enlarges in some followi…

In this chapter the apostle gives earnest exhortations to abound in holiness, with a caution against uncleanness, enforced with several arguments (Th1 4:1-8). He then mentions the great duties of brotherly love, and quietness with industry in our callings (Th1 4:9-12). And concludes with comforting those who mourned for their relations and friends that died in the Lord (Th1 4:13-18).

4:3 God’s will is for you to be holy: The foundation of Christian ethics is not philosophical speculation about virtue but doing God’s will (Rom 12:1-2; Eph 6:6; Heb 10:36; 13:20-21). Holiness (1 Thes 4:4, 7) embraces all of a person’s life (5:23); here it involves staying away from sexual sin (Greek porneia, any sexual union outside marriage).