1. The essence of Christian perfection consists in union with God by charity. While charity, by conforming our wills to God's, unites us to Him, grave sin, which directly opposes His will, produces the opposite effect. In other words, charity is the force uniting man to God, and sin the force drawing him away. Serious sin is therefore the greatest enemy of the spiritual life, since it not only injures, it but destroys it in its constituent elements: charity and grace.
This destruction, this spiritual death, is the inevitable result of sin, the act by which man voluntarily detaches himself from God, the one source of life, charity, and grace. As the branch cannot live if it is separated from the trunk, neither can the soul live if separated from God. God, the cause of every being, is always present in the soul of the sinner in the same way in which He is present in all creatures; yet He is not there as a Father, as a Guest, as the Trinity which offers Itself to the soul to be known and loved. Hence, the sinner, though created to be the temple of the Blessed Trinity, has voluntarily made himself incapable of dwelling with the three divine Persons and has barred his own road to union with God. He has, so to speak, obliged God to break all ties of friendship with him because he has preferred the temporal, fleeting good of a miserable creature - a selfish satisfaction, an earthly pleasure - instead of the sovereign good. This is the malice of sin which rejects the divine gift and betrays its Creator, Father, and Friend. "Oh! Why can we not realize that sin is a pitched battle against God with all our senses and the faculties of the soul; the stronger the soul is, the more ways it invents to betray its King" (T.J.Exc,14).
2. If we wish to have a better understanding of the evil of mortal sin, we must consider its disastrous effects. One single sin instantly changed Lucifer, the angel of light, into an angel of darkness, into the eternal enemy of God. A single sin deprived Adam and Eve of the state of grace and friendship with God, taking away all their supernatural gifts and condemning them to death together with the rest of mankind. One single sin was enough to make an abyss between God and man, to deprive the whole human race of any possibility of union with God.
The Passion of Jesus is a further proof of the great malice and the destructive power of sin. The lacerated members of Christ, His sorrowful death on the Cross, proclaim that sin is a form of deicide. Jesus, the most beautiful of the sons of men, through sin, become the "despised and the most abject of men, a man of sorrows.... He was bruised for our sins," so that "from the sole of His foot unto the top of His head, there is no soundness therein" (Isa 53, 3-5 - 1-6), for by means of it, He wished to vanquish death and restore friendship to man.
Jesus, our Head, invites us, His members, to unite with Him in His work of destroying sin: to destroy it in ourselves down to the very roots, that is, in our evil inclinations, and to destroy it likewise in His other members by allowing Him to work in us. This is the law of solidarity, for the misfortune of the others; each sin is a burden on the whole world and disturbs the equilibrium of God's plan. Therefore, every Christian, and more especially, every soul consecrated to God, must throw himself ardently into the battle against sin and fight it with the proper weapons: penance, expiatory prayer, and most of all, love. When the love of charity is perfect, it destroys sin more efficaciously than the fire of purgatory. In this we see why the saints were able to convert so many souls. God used the fire of their charity to do away with sin in sinners.
"O my God and my true Strength! How is it, Lord, that we are cowards in everything save in opposing Thee? To this the children of Adam devote all their energies. Were not reason so blind, the combined energies of all men put together would not suffice to make them bold enough to take up arms against their Creator and maintain a continual warfare against One who in a moment could plunge them into the depth....."O Lord, what hardness of heart! Oh, what folly and blindness! We are distressed if we lose anything, the merest trifle. Then why are we not distressed at losing that great Treasure which is the Majesty of God, and a kingdom in which our fruition of Him will be endless. Why is this? I cannot understand it.....I believe, Lord, that You treasure one soul that we gain for You by our prayers and works, thanks to your mercy, more than all other services that we can render You" (T.J. Exc, 12 - 14 -F, 1 - Way, 1).
After "Divine Intimacy" by Fr. Gabriel of Saint Mary Magdalen OCD.