Your iniquities have separated between you and your God, and your sins have hid His face from you that He will not hear. – Isaiah 59:2

When sin is on your conscience it needs no law to prevent your communion with God, for you cannot approach Him—you are afraid to do so, and you have a distaste for it. Until the pardoning blood speaks peace within your spirit, you cannot draw near to God! The Apostle says, “Let us draw near with a true heart in full assurance of faith, having our hearts sprinkled from an evil conscience and our bodies washed with pure water.” It is the washing which enables us to draw near. We shrink. We tremble. We find communion impossible until we are made clean.

The defilement was frequent, but the cleansing was always ready. At a certain time, all the people of Israel brought a red heifer to be used in the expiation…The red heifer was killed before the uncleanness was committed, just as our Lord Jesus Christ was made a curse for sin long, long ago. Before you and I had lived to commit the uncleanness, there was a Sacrifice provided for us. For the easing of our conscience, we shall be wise to view this sacrifice as that of a substitute for sin and consider the results of that expiation. Sin on the conscience needs, for its remedy, the result of the Redeemer’s Substitution. 

Today the Living Water of the Divine Spirit’s sacred influences must take up the result of our Lord’s Substitution and this must be applied to our consciences. That which remains of Christ after the fire has passed upon Him, even the eternal merits—the enduring virtue of our great Sacrifice—must be sprinkled upon us through the Spirit of our God. Then are we clean in conscience, but not till then. When the eternal Sabbath breaks, then shall be the last sprinkling with the hyssop and we shall be clean, and we shall enter into the rest which remains for the people of God and clean every whit! We shall come before God, at last, without spot or wrinkle, or any such thing, and be as able to commune with Him as if we had never transgressed, being presented faultless before His Presence with exceedingly great joy! ~ C.H. Spurgeon

https://www.blueletterbible.org/comm/spurgeon_charles/sermons/1481.cfm