Every believer in Christ must live a life of holiness. Our God is a holy God and we need to walk in holiness to please Him. Living a life without holiness (righteousness) will make us vulnerable to Satanic attacks. Holiness means to be set apart from sin and be morally pure. By being holy, an individual resists Satan and abstain from compromises that would give the enemy a foothold or crack in the armor.
Stand therefore, having girded your waist with truth, having put on the breastplate of righteousness
This scripture tells us that, just as a Roman soldier puts on a belt and breastplate in preparation for war, we must also put on the spiritual belt of truth and the breastplate of righteousness. A breastplate in warfare functions as a crucial torso armor which protects vital organs (heart, lungs, liver and others) from fatal blows by swords, arrows, or spears. It serves as a body shield and allows soldiers to stay in the fight even when the opposition is strong.
Biblically, the breastplate of righteousness was purchased for us by Jesus at the cross (2 Cor. 5:21). When a sinner repents and receives the salvation of God, the breastplate of righteousness is issued to him or her. It is specially designed by God to protect our hearts and souls from evil and all forms of deception which lead men away into death. Every believer in Christ must protect their hearts by ensuring their breastplate of righteousness is always on by being holy at all times and being immediately repentant when we fall.
This why we need to guard our hearts because sins - fornication,adultery, rape, murder, robbery, and the like - is resolved in the heart. When temptation comes, we decide whether to give in or stay righteous in our hearts. An unholy heart full of unrighteousness will open doors for demonic oppression in the life of a careless Christian.
While in the wilderness, Satan came against Jesus with evil arrows of the lust of the flesh, the lust of the eyes and the pride of life but He was able to resist him because of His holy lifestyle (His well strapped and adapted breastplate of righteousness). Daniel’s lifestyle of righteousness enabled his deliverance from ferocious lions that were supposed to devour him. Instead, the lions became like house pet cats and a warm pillow for the night. These two examples are in stark contrast to Samson who became vulnerable to the attacks of his enemies because of his careless lust for sexual sin. His enemies overpowered him, took his sight and turned him from an anointed spiritual and physical strong man to a corn–grinding slave, comparable to a work horse. What a sad case!
Dear friend, the breastplate of righteousness has been given to you as a believer in Christ. Always have it on because Satan is on the lookout for careless Christians who he can oppress and it is a crucial, non-negotiable defence God has given you to ensure constant victory over Satan's evil works.