Explanation of the text: 1 Thess. 4:3-5 Purity of Life

1Th 4:3  For this is God's will--your purity of life, that you abstain from fornication; 
1Th 4:4  that each man among you shall know how to procure a wife who shall be his own in purity and honour; 
1Th 4:5  that you be not overmastered by lustful cravings, like the Gentiles who have no knowledge of God; 

Notes: For this is God's Will - your Sanctification, for you to be at a distance from all harlotry

God's Will: [thelema]: Determination;choice, purpose, decree, desire and pleasure.

ἁγιασμός hagiasmos Thayer Definition:

1) consecration, purification

2) the effect of consecration

2a) sanctification of heart and life.

Strong's From G37; properly purification, that is, (the state) purity; concretely (by Hebraism) a purifier: - holiness, sanctification.

" Internal Sanctification (the setting apart of heart and life as holy and for God alone) is the work of the Spirit of God.

It is a principle of the Spiritual life of the soul, where the Divine and Spiritual Light of God enters the understanding and now the life is a reflection of the Will of God. There is a Divine Rest in all the affections and an implantation of every grace in the heart and mind of the believer."

 External Sanctification arises from the above and is manifested by Holiness in life and all conversation." Bible Illustrator.

"This is the Will of God for each one of us.. This is His purpose and decree. As the Salvation of the Soul so the Sanctification of the heart and life. " John Gill

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that you abstain from fornication;

[porneia] = 

Thayer Definition:

1) illicit sexual intercourse

1a) adultery, fornication, homosexuality, lesbianism, intercourse with animals etc.

1b) sexual intercourse with close relatives; Lev. 18

1c) sexual intercourse with a divorced man or woman; Mar_10:11,Mar_10:12

2) metaphorically the worship of idols

2a) of the defilement of idolatry, as incurred by eating the sacrifices offered to idols

1Th 4:4  that each man among you shall know how to procure a wife who shall be his own in purity and honour; WNT

1Th 4:4  Each of you should know that finding a husband or wife for yourself is to be done in a holy and honorable way, GW.

Notes v.4.

RWP comments:

That each one of you know how (eidenai hekaston humōn). Further epexegetic infinitive (second perfect active), learn how and so know how (learn the habit of purity). 

- how to procure a wife who shall be his own in purity and honour; 

- To possess himself of his own vessel (to heautou skeuos ktasthai).  "Present middle infinitive of ktaomai, to acquire, not kektēsthai, to possess. But what does Paul mean by “his own vessel”? It can only mean his own body or his own wife. Objections are raised against either view, but perhaps he means that the man shall acquire his own wife “in sanctification and honour,” words that elevate the wife and make it plain that Paul demands sexual purity on the part of men (married as well as unmarried). There is no double standard here. When the husband comes to the marriage bed, he should come as a chaste man to a chaste wife."RWP.

1Th 4:5  that you be not overmastered by lustful cravings, like the Gentiles who have no knowledge of God; WNT

Not in passionate lust ;like the heathen, who do not know God. NIV.

Notes:in the lust — Greek, “passion”; which implies that such a one is unconsciously the passive slave of lust.
which know not God — and so know no better. Ignorance of true religion is the parent of unchastity (Eph_4:18, Eph_4:19). A people’s morals are like the objects of their worship (Deu_7:26; Psa_115:8; Rom_1:23, Rom_1:24).

 Or "passion of lust"; for the mere gratifying and indulging of that; for a man so to possess his vessel, is to cherish the sin of concupiscence, the first motions of sin in the heart, by which a man is drawn away, and enticed; to blow up the flame of lust, and to make provision for the flesh to fulfil the lusts thereof:

CONCUPISCENCE, n. [L., to covet or lust after, to desire or covet.] Lust; unlawful or irregular desire of sexual pleasure. In a more general sense, the coveting of carnal things, or an irregular appetite for worldly good; inclination for unlawful enjoyments.

We know even secret concupiscence to be sin.

 Holiness is not just for advanced Christians but stands at the beginning and center of God's call on all of our lives: "Be holy, because I am holy" . Christianity Today.