I will greatly rejoice in the LORD, my soul shall be joyful in my God; for He hath clothed me with the garments of salvation, He hath covered me with the robe of righteousness, as a bridegroom decketh himself with ornaments, and as a bride adorneth herself with her jewels. – Isaiah 61:10

Some of you have to live in smoky, grimy London, but the smoke and the grime cannot discolour the spotless robe of Christ’s righteousness. In yourselves, you are stained with sin; but when you stand before God, clothed in the righteousness of Christ, the stains of sin are all gone… The believer in Christ is as pure in God’s sight at one time as he is at another. He does not look upon the varying purity of our sanctification as our ground of acceptance with Him; but He looks upon the matchless and immutable purity of the person and work of the Lord Jesus Christ, and He accepts us in Christ, and not because of what we are in ourselves. Hence, when we are once “accepted in the Beloved,” we are permanently accepted; and being accepted in Him, we are “whiter than snow.”

Further, the whiteness of snow is, after all, only created whiteness. It is something which God has made, yet it has not the purity which appertains to God Himself; but the righteousness which God gives to the believer is a divine righteousness, as Paul says, “He hath made Him to be sin for us, who knew no sin; that we might be made the righteousness of God in Him.” And remember that this is true of the very sinner who before was so black that he had to cry to God, “Wash me, and I shall be whiter than snow.” ~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/3278.cfm