How can God be both just and justify sinners?

John Latham explains in this video that one of the great mysteries that we grapple with and one of the most joyful truths in Scripture is that God can justify the ungodly guilty. To justify involves the declaring of one being innocent.  

For God to be able to look at us and say that a person is not guilty is one of the great mysteries of Scripture. How does He do it? He does it through His Son. The great truth of the Gospel is that what we could not do for ourselves, God did it through His Son.  

Romans 3:23-26 (NKJV) – “for all have sinned and fall short of the glory of God, being justified freely by His grace through the redemption that is in Christ Jesus, whom God set forth as a propitiation by His blood, through faith, to demonstrate His righteousness, because in His forbearance God had passed over the sins that were previously committed, to demonstrate at the present time His righteousness, that He might be just and the justifier of the one who has faith in Jesus.”

One of the great mysteries that we grapple with, one of the truths that we rejoice in and yet is difficult is that God can justify the ungodly. To justify means to declare innocent and not in a way that an unrighteous judge might do and declare someone who is truly guilty not guilty. But for God to be able to look at us And to say, no, this one truly is not guilty, is one of the great mysteries and yet the great truths of Scripture. And yet how does he do that? He does it through his Son.

God through the just justifies the ungodly. The great truth of the gospel is that what we could not do for ourselves, God did through His Son. That the price that needed to be paid, He paid. The life we had to live to be right with God, He lived. So that by faith in Christ we are united to Him, so the Scripture speaks of us as being clothed in His righteousness.

Because we are in Christ, God can truly look upon us and justify us and say, Not guilty. Not guilty. This one is blameless and holy before me because of what my son has done and because they are united to him by faith.