Have Ye Not Read?
Question: Is it a sin to wear very conservative shorts and bathing suits? If so, where do you draw the line on what is modest, and who is to judge?
Reply: It is presumed that our querist is referring to wearing shorts and bathing suits in public.
God desires that mankind be clothed, as opposed to the modern nudists and hedonists who advocate "freedom" and "naturalness" while they openly display their bodies. God Himself provided clothing to cover the first man and woman (Gen. 3:21).
Christians are to dress in modest apparel. Paul instructed women to adorn themselves in modest apparel (1 Tim. 2:9). The word "modest" is the Greek word kosmios, which according to W.E. Vine, means "orderly, well-arranged, decent, modest" (Expository Dictionary of Greek Words, Vol. 3, p. 79). Arndt and Gingrich define it "respectable, honorable" (Greek-English Lexicon, p. 446). The idea is that a Christian is to dress orderly, decently, modestly and with respect; and it applies to both men and women. It is not modest and respectable to parade about on the streets in short attire, nakedness being in plain view to the public eye. Such behavior is unbecoming of Christians. It is incompatible with Bible teaching. Paul wrote in Titus 2:11, 12, ". . . for the grace of God hath appeared, bringing salvation to all men, instructing us, to the intent that, denying ungodliness and worldly lusts, we should live soberly and righteously and godly in this present world . . . ." The world approves of halter tops and bikinis but this standard does not make them acceptable for Christians. 1 Timothy 2:9 should be the guideline for the Christian's apparel - it should be modest.
Another word in 1 Timothy 2:9 which deserves our attention is the word "shamefastness" (ASV), "shamefacedness" (KJV), translated from the Greek word aidos. Thayer defines it as "a sense of shame, modesty" (Greek-English Lexicon, p. 14). When these two words are considered, there can be no doubt that the wearing of shorts, bikinis, halter tops and such like in public are condemned by the word of God.
As to how we are to draw the line on what is modest, common sense must be applied in light of what the word of God teaches. When this is done, there will be no question in one's mind as to what is modest and what is immodest. This same rule applies as to what is moral and immoral, decent and indecent, whether it be entertainment, recreation, speech or whatever. The business of the Christian is to serve God in truth and sincerity, and to do nothing that is questionable or that will bring any reproach upon his character. Paul expressed the aim of every devoted child of God when he wrote, "that ye may become blameless and harmless, children of God without blemish in the midst of a crooked and perverse generation, among whom ye are seen as lights in the world" (Phil. 2:14, 15).
Guardian of Truth XXVII: 1, p. 23