In the Bible it is written, "Moreover the law entered, that the offence might abound. But where sin abounded, grace did much more abound: that as sin hath reigned unto death, even so might grace reign through righteousness unto eternal life by Jesus Christ our Lord." (Rom 5:20-21)
This text is comparing two forces: as sin reigns by and unto death, so grace reigns by and unto righteousness. In other words, in a comparable way that the sin nature has gained control, establishing dominion in many souls and bringing them into disobedience, rebellion, corruption and alienation from God, similarly grace has also gained control, establishing dominion in many souls by working righteousness in them and bringing them into eternal fellowship and intimacy with God.
Both sin and grace are real forces or natures at work within Mankind, not merely abstract concepts. If we consider this carefully, we will see that the above verse is not so much a comfort to those who have sinned greatly as it is a rich promise from God to those seeking holiness in the midst of a profoundly sinful world.
To help us see this more clearly, it is certainly helpful to understand the definition of grace: "divine influence upon the heart and its manifestation in the life." (Strong) When we hear the word grace we should think divine power, supernatural enablement. This is much different than mercy, a concept we often confuse with grace, and in such confusion attempt to claim from texts such as this that the more one sins the more grace God gives by forgiving. Yet the text does not say, "where sin abounded, forgiveness and mercy did much more abound." Grace is not Forgiveness, nor is it Mercy: we must not confuse the terms. (See also Not Under the Law, But Under Grace)
When we hear grace reigns through righteousness we ought not to think that God in mercy and forgiveness is making many people positionally righteous in spite of their profound sinfulness. Though this is certainly true, it is not the intent of the text. We ought rather to see here that the life of God so moves in His children that they actually grow in practical holiness as a manner of life even if they are in very difficult, sinful or perverse circumstances. If we persist in thinking grace is merely forgiveness, leniency or mercy we miss the rich implications and promises in texts such as this, which would help us see that the life of God gives us power to live for Him regardless what the world might bring upon us. It is in this sense that grace reigns through righteousness: not merely a theoretical righteousness and an abstract reigning, but a practical reality, a legitimate overcoming and control that the grace of God brings in His elect to conform them to Himself.
Sin reigns in the lives of those who are unregenerate, moving them to despise the laws of God and reap the eternal consequences: corruption and alienation from divine life. This is "the law of sin and death," (Rom 8:2b) operating out of and springing from the central nature of all who are not of God. But as children of light, children of the Day (1Th 5:5), we who have been born again, have working continually within us "the law of the Spirit of life in Christ Jesus," (Rom 8:2a) making us free from the law of sin and death. We have access by faith to the grace that enables us to overcome, moving and strengthening us to love, honor and obey God even when all around us the wicked are spitting in His face.
No matter how corrupt the world becomes, God's grace reigns in His elect, empowering and overcoming, and evidently more so in the midst of extreme perversion and moral decay. Let us be established with grace, knowing that as the enemy seeks to silence, extinguish and trample us underfoot, the light of God shines the more brightly in and through us. The worse things get around us the more clearly God's power becomes evident to enable us to live for and rejoice in Him. Fear not: "In all these things we are more than conquerors through Him that loved us." (Rom 8:37)