The prophet Jeremiah asks two possibly rhetorical questions, to illustrate that it is impossible for sinners (those accustomed to do evil), which is you and I, to be saved by our own accord.
The questions recorded in Jeremiah 12:23 are 1. Can the Ethipioan change his skin and 2. Can the leopard change his spots?

Think about this, can a leopard change his spot? Likewise, we cannot rid ourselves of our sinful habits (sins’ dark spots), except by the grace and mercy of the Lord Jesus Christ. Jesus can make you spotless clean.
For a tow truck to be able to pull a defunct vehicle, it’s engine needs to be more powerful to pull the weight of the vehicle. There is power in Jesus and no matter how heavy our sins and situations are, He can pull you through.

So ask God today to be THE Strength, to overcome sinful habits that hold us in bondage. We cannot do it on our own, save by Jesus alone, for He paid it all.

Lord, now indeed I find. Thy pow’r, and Thine alone,
Can change the leopard’s spots And melt the heart of stone.
Jesus paid it all, All to Him I owe;
Sin had left a crimson stain, He washed it white as snow.

Jeremiah 12:23
      Can the Ethiopian change his skin, or the leopard his spots? the may ye also do good, that are accustomed to do evil.