The scale we understand: your good deeds are placed on one side and your bad deeds are placed on the other side. If the scale tips toward the bad side, the sword in her other hand is for punishing the guilty. But most of us are pretty sure the sword won't be necessary in our case! Most religions are merit based: what happens to you in life and in whatever judgment follows this life depends on what you have earned by your deeds. Making it into paradise, according to Islam, depends on doing what is required. Hinduism, with its inviolable law of Karma, views everything in terms of merit. Christians should know better, but we often talk like acceptance with God depends on what we do.
As I was talking about this recently with my son, he said, "So Christianity is the only religion not based on merit, right?" I said, "No. Christianity is based on merit, too." I paused for a minute as he looked at me like I had lost my mind. Then I said, "It's based on Christ's merit, not yours."
We sing: When Satan tempts me to despair and tells me of the guilt within, upward I look and see Him there, who made an end to all my sin. Because the sinless Savior died my sinful soul is counted free, for God the just is satisfied to look on him and pardon me.
The good news of the gospel is not that God forgives your sin by just ignoring it or pretending it doesn't matter. God is not an unjust judge. Sin must be punished. That's why Jesus came into the world. God's love is demonstrated in giving His Son to die in the place of guilty people. God offered Jesus as a substitute. Our sin was credited to him and the sword of justice came down on him. Lady Justice, with her scale and sword, is a symbol. God is the ultimate reality! God, the just, punished Jesus in our place, and God credited his righteousness to us. God remained just and was able to justify all those who are united to Christ by faith.
When it is time for you to stand before God, you don't have to be afraid of the sword. When you are united to Christ by faith, there's no unrighteousness left to weigh down the scale of justice in your case. Instead, there's an infinite supply of righteousness credited to you that pulls the scale down on that side. The sword of justice will not be necessary in your case because it has already come down on Jesus, who took your place.
Our salvation is based on merit and absolute justice. That's what the cross is all about! Christ made an end to all our sin in his death on the cross. The demands of justice are satisfied by Jesus, not by anything we do. That's why we can say that salvation is God's work from beginning to end. That's why we talk about grace! It is the work of Jesus that saves.