The famous monk of the Reformation, Martin Luther, coined the Latin phrase, "simul justus et peccator." It roughly translates into: simultaneously just and sinner. It means that we, as Christians, are made righteous, yet at the same time we are still prone to the righteousness of sin.
How does that work?
I have personally been helped by 1 John 5:16-20. In this passage, John distinguishes venial sins versus mortal sins. When an unbeliever sins, it is a mortal sin. God will not stand idly by when people deny, disregard and disobey him. So, for the one who commits mortal sins, the penalty is death (Romans 6:23).
Christians, on the other hand, are made righteous and justified by Christ (Galatians 5:15-21). When Jesus died for us, he took our sin and gave us his righteousness (2 Corinthians 5:21). Because of this, we are not condemned, but justified. Our sin no longer leads to death; rather, it is Christ's righteousness that leads to eternal life.
Thus, when the Christian sins, it is a venial sin. In other words, though the act of sinning is unrighteous and an offence against God, it does not change our justification. Because of Jesus, we will always be righteous before God.
1 John 5:16-20 reminds us that the effects of sin will plague us in this life. Justification is a completed work. But being declared righteous does not mean that we have been perfected in righteousness just yet (Philippians 1:6). That is why God also promises to sanctify us (1 John 1:9). We are no longer enslaved to sin (Ephesians 6:6) or the Satan's machinations (1 John 5:18). We don't have to keep sinning because God's Spirit is changing us!
So, yes, we are justified. But, for now, we will struggle with sin. That is how we are "simul justus et peccator."
Simul Justus et Peccator
