For if the blood of bulls and of goats, and the ashes of an heifer sprinkling the unclean, sanctifieth to the purifying of the flesh: How much more shall the blood of Christ, who through the eternal Spirit offered Himself without spot to God, purge your conscience from dead works to serve the living God? – Hebrews 9:13,14

The purifying power of the blood of Christ must be much greater than the purging power of the water mixed with the ashes of the heifer, for, first, that could not purge conscience from sin, but the application of the Atonement can and does do it. Did you ever feel the Atonement of Christ applied by the Holy Spirit to your conscience? Then I am certain of it that the change upon your mind has been as sudden and glorious as if the darkness of midnight had glowed into the brightness of noonday!

I remember well its effects upon my soul at the first—how it broke my bonds and made my heart dance with delight! But I have found it equally powerful since then, for when I am examining myself before God, it sometimes comes to pass that I fix my eyes upon some one evil which I have done and I turn it over until the memory of it eats into my very soul like caustic acid, or like a gnawing worm, or like coals of fire! I have tried to argue that the fault was excusable in me, or that there were certain circumstances which rendered it almost impossible that I could do otherwise. But I have never succeeded in quieting my conscience in that fashion! Yet I am soon at rest when I come before the Lord and cry, “Lord, though I am Your own dear child, I am unclean by reason of this sin! Apply, again, the merit of my Lord’s atoning Sacrifice, for have You not said— “If any man sin, we have an Advocate with the Father, Jesus Christ the Righteous?”

Lord, hear His advocacy and pardon my offenses!” My Brothers and Sisters, the peace which thus comes is very sweet. You cannot pray acceptably before that peace and you may thank God that you cannot, for it is a dreadful thing to be able to go on with your devotions under a sense of guilt as when the conscience is at rest! ~ C.H. Spurgeon

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