Jeremiah 13:23 - Our Fallen Natures Need Jesus for Healing.

Jer 13:23 (KJV)  Can the Ethiopian change his skin, or the
leopard his spots? then may ye also do good, that are accustomed to do
evil.

Jer 13:23 (NIV)  Can the Ethiopian change his skin or the
leopard its spots? Neither can you do good who are accustomed to doing
evil.

Jer 13:23 (TEV)  Can a black man change the color of his skin,
or a leopard remove its spots?  If they could, then you that do
nothing but evil could learn to do what is right.

The question is rhetorical: Can a black person change the color
of his skin or a leopard its spots? The answer is clearly no.
[Jamieson, Fausset, And Brown Commentary]

The passage shows how difficult it is for anyone to liberate
himself from the innate tendency to sin. [Expositors Bible Commentary]

   A scorpion, being a very poor swimmer, once asked a turtle to
carry him across a river on his back. "Are you mad?" exclaimed the
turtle. You'll sting me while I'm swimming and I'll drown."
   The scorpion laughed as he replied, "My dear turtle, if I
were to sting you, you would drown and I would go down with you. Now,
what would be the point of that? I won't sting you. It would mean my
own death!"
   The turtle thought about the logic of the scorpion's argument
for a moment, then said, "You're right. Hop on!" The scorpion
climbed aboard and halfway across the river, he gave the turtle a mighty
sting.
   As the turtle began to sink to the bottom of the river with
the scorpion on its back, it moaned in dismay, "After your promise,
you still stung me! Why did you do that? Now we're both doomed!"
The drowning scorpion sadly replied, "I couldn't help it. It's
my nature to sting." [God's Little Devotional Bible]

This people are so accustomed to doing evil that they don't even
know how to do good! [The 365-Day Devotional Commentary]

When a person becomes "accustomed to doing evil" sin becomes a
habit. [Victor Bible Reader's Companion]

Custom in sin is a very great hindrance to conversion from sin.
The disease that is inveterate is generally thought incurable. Those
that have been long accustomed to sin have shaken off the restraint
of fear and shame; their consciences are seared; the habits of sin
are confirmed; it pleads prescription; and it is just with God to
give those up to their own hearts' lusts that have long refused to
give themselves up to his grace. (Matthew Henry's Commentary)

God never rejects those who sincerely turn to him. God is
warning them to repent before it becomes impossible to change. We must
never put off until tomorrow those changes God wants us to make. Our
attitudes and patterns for living can become so set that we will lose all
desire to change and will no longer fear the consequences.  [Life
Application SB]

Sin is not a harmless companion we can drop at will. [Disciple SB]

Here is set forth the futility of any human endeavor to overcome
evil apart from the power of God. [SDA Commentary]

The proverb did not mean it was impossible for the people to
change, but that they could not hope to reform on their own. God alone
could work such miraculous changes. [Quest SB]

Sin is the blackness of the soul; it is the discolouring of it;
we were shapen in it, so that we cannot get clear of it by any
power of our own. But Almighty grace is able to change the Ethiopian's
skin. Neither natural depravity, nor strong habits of sin, form an
obstacle to the working of God. [Matthew Henry Commentary]

We often try to change by making resolutions to do what we know
to be right. But change doesn't happen overnight, and we don't have
the power to do it alone. Taking action is a good thing to do, but
if we set out to change in our own power, we will be sure to fail.
Our actions will produce no lasting changes in our life. We must
begin by admitting that we are powerless to change. This is the first
step toward allowing God to transform our heart and life from the
inside out. If we are willing to cooperate, God can and will make
permanent changes in our Life. [Life Recovery SB]

When the soul surrenders itself to Christ, a new power takes
possession of the new heart. A change is wrought which man can never
accomplish for himself. It is a supernatural work, bringing a supernatural
element into human nature. The soul that is yielded to Christ becomes
His own fortress, which He holds in a revolted world, and He intends
that no authority shall be known in it but His own. A soul thus kept
in possession by the heavenly agencies is impregnable to the
assaults of Satan. But unless we do yield ourselves to the control of
Christ, we shall be dominated by the wicked one. We must inevitably be
under the control of the one or the other of the two great powers that
are contending for the supremacy of the world. It is not necessary
for us deliberately to choose the service of the kingdom of darkness
in order to come under its dominion. We have only to neglect to
ally ourselves with the kingdom of light. If we do not co-operate
with the heavenly agencies, Satan will take possession of the heart,
and will make it his abiding place. The only defense against evil is
the indwelling of Christ in the heart through faith in His
righteousness. Unless we become vitally connected with God, we can never resist
the unhallowed effects of self-love, self-indulgence, and temptation
to sin. We may leave off many bad habits, for the time we may part
company with Satan; but without a vital connection with God, through the
surrender of ourselves to Him moment by moment, we shall be overcome.
Without a personal acquaintance with Christ, and a continual communion,
we are at the mercy of the enemy, and shall do his bidding in the
end.  DA324

Jer. 17:9 (KJV) The heart is deceitful above all things, and
desperately wicked: who can know it?

Heb. 10:16 (KJV) This is the covenant that I will make with them
after those days, saith the Lord, I will put my laws into their
hearts, and in their minds will I write them;

Rev. 3:20 (KJV) Behold, I stand at the door, and knock: if any
man hear my voice, and open the door, I will come in to him, and
will sup with him, and he with me.