The word justified means just as if you never sinned and that happens to you when you put your faith in Jesus Christ.
The fact is that you have sinned and there is nothing you can do about it except believe in Jesus and receive Him as your Savior. When you receive Him, He permanently joins Himself to your spirit, paying for your sin, forgiving you for everything, giving you eternal life and no one or nobody can take any of that away from you plus you have peace with God. That’s big-time – you were born His enemy but now the war is over, you have a perfect relationship with Him. All of this is through our Lord Jesus Christ who went to the cross taking our sin upon Himself and then washing it away with His sinless blood, making you His child.
Christmas makes all of this possible because at Christmas Jesus took on Himself a human body that could die and resurrect transforming it into a life-giving Spirit that eternally indwells every born-again believer.
Suddenly you have peace with God through Jesus and that means the merriest Christmas of all!