“…if anyone sins, we have an Advocate with the Father, Jesus Christ the righteous. And He Himself is the propitiation for our sins, and not for ours only but also for the whole world.”
The minimization of sin is the tendency of our mortal nature. “It can’t be that bad.” “All I did was… “
In the history of the church, different categorizations of sins came about. Some may even recall hearing about some of these, for example, mortal sins and venial sins.
Mortal sins were understood to be “larger” or “more damning” sins than venial, which came to be understood as less so.
However, in making any such distinctions of sin, it must be remembered that sin before God is sin, regardless of how you define it. St. Paul makes no fine distinction between greater or less sins when he writes, “The wages of sin is death” (Romans 6:23).
Sin before God is not of a greater or lesser degree. It is sin, transgression and disobedience against the most Holy God (Romans 3:20; James 1:15; 1 John 3:4). And its wages (reward) is eternal death.
Such reward is what we all deserve, for any sin is really sin against the Holy God Himself (see 2 Samuel 12:13). Therefore, it is not “the size” of the sin in our eyes by which we are condemned, but because of “the Who” whom we sin against.
Should we minimize or lessen our sin, we at the same time minimize or lessen our Savior, Jesus Christ. Yet, we do “have an Advocate with the Father, Jesus Christ the righteous.” Jesus did not pay the penalty of a “little” sin, or one or two. He sacrificed Himself for the sins of the world, even for all of your sins (1 Corinthians 5:7; Hebrews 9:11-15, 24-28).
Jesus is not a partial Savior. He is a complete Savior, whose blood covers all of your sin. The Savior you have in Jesus is sufficient to cover all that you have done, do, and will do, for Jesus is greater than your sin. As great as your sin is, Jesus is all the more your Savior.
Consider this statement of Luther “In the sight of God sins are truly venial when they are feared by men to be mortal.” (Heidelberg Disputation of 1518, Thesis 12). 
Should you see your sins as they are before God, so will you repent and look to Christ. Then your sins will not hurt you.
However, should you see your sins only as little, as defined by you or by the world, so you do not see Christ aright, and your sin will be held against you.
“Our sins are so great, so infinite and invincible, that the whole world could not make satisfaction for even one of them. Certainly the greatness of the ransom—namely, the blood of the Son of God—makes it sufficiently clear that we can neither make satisfaction for our sin nor prevail over it. The force and power of sin is amplified by these words: “Who gave Himself for our sins.” We are indifferent, and we regard sin as something trivial, a mere nothing. Although it brings with it the sting and remorse of conscience, still we suppose that it has so little weight and force that some little work or merit of ours will remove it. But we should note here the infinite greatness of the price paid for it. Then it will be evident that its power is so great that it could not be removed by any means except that the Son of God be given for it. Anyone who considers this carefully will understand that this one word “sin” includes the eternal wrath of God and the entire kingdom of Satan, and that sin is no trifle.” (Luther’s Lectures on Galatians, LW 26, p33).
Prayer: Heavenly Father, look not upon my indifference to your law and my sin before You. Incline Your ear to me for the sake of Your only begotten Son. Forgive me for my disregard and my little concern for offending Your Holy majesty. Bring me to right repentance and firm trust in Your compassionate mercy, that I believe Christ rightly and abide in Your presence for all eternity. Amen.
Martin Luther, vol. 31, Luther’s Works, Vol. 31 : Career of the Reformer I, ed. Jaroslav Jan Pelikan, Hilton C. Oswald and Helmut T. Lehmann, Luther’s Works (Philadelphia: Fortress Press, 1999, c1957).