ISB ~ 1 Thessalonians 4 v3

sanctification:Holiness of life is willed by God. Growth in holiness, or progressive sanctification, is a process that begins with God’s work in Baptism (1 Cor 6:11) and continues when believers abound in love (1 Thess 3:12-13) and exert the moral effort needed to overcome sinful and selfish habits (Rom 6:19). Paul here demands the sanctification of the body through chastity, though the ultimate goal is a complete sanctification of the person (1 Thess 5:23). Holiness is not optional for believers but is a condition for salvation (Heb 12:14) (CCC 2348-50, 2813).

• Vatican II issued a universal call to holiness for clergy and laity alike that is expressed through the perfection of love (Lumen Gentium 39).

abstain from immorality:Specifically, from the various forms of sexual immorality widely accepted in pagan environments such as Thessalonica. The Greek expression used here is also found in the apostolic decree issued by the Jerusalem Council in A.D. 49 (Acts 15:20, 29). Paul, Silas, and Timothy (1 Thess 1:1) went about delivering this decree on the second missionary tour in Acts (Acts 16:4). See note on Acts 15:20.