And whosoever toucheth one that is slain with a sword in the open fields, or a dead body, or a bone of a man, or a grave, shall be unclean seven days. – Numbers 9:16

The Israelite became unclean even in the act of doing good, for assuredly it was a good deed to bury the dead! A man would be defiled, if, out of charity, he helped to inter the poor, or the slain, or the poor relics of mortality which might be exposed upon the plain—and yet this was a praiseworthy action. Alas, there is sin even in our holy things. A morality so pure that no human eye can detect a flaw may yet be faulty to the eye of God. Brothers and Sisters, sin stains our piety and pollutes our devotion! We do not even pray without needing to ask God to forgive the prayer. Our acts of faith have a measure of unbelief in them, for the faith is never so strong as it ought to be. Our penitential tears have some grit of impenitence in them and our heavenly aspirations have a measure of carnality to degrade them. The evil of our nature clings to all that we do. Who shall bring a clean thing out of an unclean? No one! One way or another defilement will come upon us. We have been once washed in the blood of Jesus, and we are clean before the bar of God. And yet in the Divine family we need that our feet be washed after walking awhile in this dusty world and there is not one disciple who is above the need of this washing. To one and all our Lord says, “If I wash you not, you have no part in Me.”

Pollution went forth from the polluted. Do you and I sufficiently remember how much evil we are spreading when we are out of communion with God? Every ungenerous temper creates the same in others. We never cast a proud look without exciting resentment and bad feelings in others. Somebody or other will follow our example if we are slothful—and thus we may be doing great mischief even when we are doing nothing! You cannot even bury your talent in a napkin without setting an example to others to do the same and were that example followed by all, how dreadful would be the consequences! Observe that I am not now speaking of sinners, but of the saints of God! My soul’s longing is that we may walk worthy of the Lord unto all well-pleasing and may not become unfit for communion with Him.  ~ C.H. Spurgeon

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