A small view of sin results in a small view of the Gospel.
If our understanding of depravity is that we do bad things (or fail to do the right things), we focus only on sins in the plural. In that understanding, sin is tied to behaviors or actions that we do or don’t do. And certainly those sins are abhorrent to God (Proverbs 6:16-19, Galatians 5:19-21, etc.). But sin is bigger than acts of sinning.
Scripture speaks of sin as the nature that we as human beings are born with (Romans 7:18). It is what comes naturally out of our hearts apart from Christ. It is what makes us enemies of God who are destined to receive His wrath (Romans 5:10, Ephesians 2:3). It is the constant inclination of our hearts away from God (Genesis 6:5).
That sin is so pervasive that even our seemingly righteous acts can come out of a heart that is set on autonomy from God (Isaiah 64:6). Martin Luther coined a phrase that aptly depicts this pervasive sin in our hearts: incurvatus in se. This Latin phrase means “curved in on oneself.” The essence of our sin is that we try to save ourselves–we try to make life work apart from God.
When we begin to grasp the depth of that sin, and when we begin to realize that even our virtue is clouded with self-salvation efforts, we can cry out with Paul in Romans 7:24, “Wretched man that I am! Who will deliver me from this body of death?” But it is that cry of wretchedness that then opens the door to exclaim in great joy with Paul, “Thanks be to God through Jesus Christ our Lord!” (Rom. 7:25)
Seeing sin in all its ugly depth allows us to see the Gospel in all its wonder and beauty.