Having studied the various lists of prohibitions for Christians in the New Testament, I think it is helpful to focus on four major arenas Christians must fight for separation from sin: sexual purity, speech purity, relational purity, purity in lawful pleasures.
1) Sexual Purity
Few areas have the power to destroy with as much devastating power as sexuality. It is clearly a tremendous weakness in the armor of our souls. Because of the significance and sacredness of sex, Satan has concentrated much of his efforts on polluting us in this one arena. Therefore, mature Christians are constantly vigilant lest they should fall sexually: “Flee from sexual immorality. All other sins a man commits are outside his body, but he who sins sexually sins against his own body” (1 Cor. 6:18). Mature Christian men make covenants with their eyes not to look lustfully at women (Job 31:1), because to do so is like committing adultery with her in the heart (Matt. 5:28). We must be especially vigilant in the area of Internet pornography, which makes sexual immorality easier than it has ever been in history. Likewise, Christian women must guard their own hearts from adultery, from the lure and excitement of a new relationship, from intimacy with a man who is not her husband, or from fantasizing through romance novels or movies. Furthermore, a mature Christian woman will understand the power of her body, the allure of her beauty, and dress modestly (1 Tim. 2:9). Too many Christian men and women have been destroyed by sexual sin. It is a dangerous thing, with the power to destroy households, churches, mission agencies, and even lives. So, utmost caution must be exercised at all times.
"Few areas have the power to destroy with as much devastating power as sexuality."
2) Purity in Speech
According to James, no member of the body causes so much pain, so much anguish as the tongue, and no member is so hard to control. Therefore, a certain sign of Christian maturity is purity of speech: “If anyone is never at fault in what he says, he is a perfect man, able to keep his whole body in check” (James 3:2). Thus Scripture gives us this prayer: “Set a guard over my mouth, O Lord; keep watch over the door of my lips” (Psalm 141:3). Think of a water filtration system, which can remove particles, sediment, dissolved metals, bacteria, and other contaminants, resulting in water purified to an exacting specification. Ephesians 4:29 is the ultimate “word filter” in the entire Bible. Anything that does not meet the specification laid down in that one verse must be filtered out from my speech: “Let no corrupting talk come out of your mouths, but only such as is good for building up, as fits the occasion, that it may give grace to those who hear” (Eph. 4:29, ESV). Words that corrupt include: arguing, blasphemy, boasting, complaining, cursing, disrespect, false doctrine, filthy joking, flattery, gossip, insults, lies, mockery, slander, threats, words of unbelief, etc. Words that give grace include: the gospel message, right doctrine, encouragement, praise and thanksgiving to God, prayer, godly counsel, talk of heavenly pleasures, etc.
3) Purity in Relationships
A mature Christian strives constantly to love others as himself in obedience to the second Great Commandment (Matt. 22:39). In order to do this, he must purify himself of all defiling attitudes and behaviors listed in Galatians 5: “hatred, discord, jealousy, fits of rage, selfish ambition, dissensions, factions and envy” (Gal.5:20-21). At the core of all of these are the root sins of pride, anger, and unforgiveness. Pride is the underlying cause of all wars, all marital squabbles, all lawsuits, all luxury and all poverty, all addictions, all parenting struggles, all church splits, all vaunting ambition, basically all trouble between human beings. A mature Christian seeks to grow in humility toward others. Such maturity also gives special attention to anger, since it is almost always born from the parents of pride and selfishness. James commands us to get rid of anger, calling it “moral filth” (James 1:19-21). A spiritually mature Christian will also purify himself of unforgiveness and all of its connected sins (Matt. 18:21-35). A mature Christian will purify his heart from all bitterness, rage and anger (Eph.4:31), and from the defiling actions that result. He will strive to keep his life free from broken relationships due to unforgiveness. He will abstain from revenge, hostility, power plays, cliques, backbiting, and other such things that destroy relationships.
"At the core of all of these are the root sins of pride, anger, and unforgiveness."
4) Purity in Lawful Pleasures
At no time in history have Christians had so many lawful diversions from the work of the Kingdom, and (seemingly) so much time with which to enjoy them. I am speaking of those good gifts given by God for us richly to enjoy and from which we must constantly guard our hearts lest we become ensnared by them: food, drink, sleep, hobbies, entertainments, vacations, possessions, sports, and so forth. The tendency of our restless hearts is to take created things and lift them up to fill a role that was meant for God alone, and that is idolatry (Rom. 1:25). In this matter of the enjoyment of lawful pleasures, there are two extremes to which we are constantly tempted to go. On the one hand, we are tempted by deny all sensory pleasure by believing that the physical body is intrinsically evil. On the other, we are tempted to indulge in God’s gifts to the point of gluttony and enslavement. Perhaps the most important verses addressing our need for purity in lawful pleasures are found in 1 Corinthians: “‘Everything is permissible for me’—but not everything is beneficial. ‘Everything is permissible for me’—but I will not be mastered by anything. ‘Food for the stomach and the stomach for food’—but God will destroy them both” (1 Cor. 6:12-13). Paul was determined not to become enslaved by addiction to the good gifts of God. To eat, but not be a glutton. To sleep, but not be a sluggard. To enjoy sports, but not become mastered—enslaved—by them. God commands wisdom and balance in the matter of lawful pleasures. Love your spouse, play with your children and grandchildren as they grow, sit with your aging and ailing parents while there is time, enjoy your job, dabble in a hobby, watch a game or two, see a movie, own some things, eat your favorite entrée with relish. But watch yourself closely lest any of these things take over and become the master rather than the servant of your soul.
The actions of a mature Christian must be pure, free from defilement of any kind. It is only as we keep ourselves pure in these areas that our lives will be pleasing to God.