"But the firstling of an ass thou shalt redeem with a lamb:  and if thou redeem him not, then shalt thou break his neck."  Exodus 34:20

Every firstborn creature must be the Lord's, but since the ass was unclean, it could not be presented in sacrifice.  What then?  Should it be allowed to go free from the universal law?  By no means.  God admits of no exceptions. The ass is His due, but He will not accept it; He will not abate the claim, but yet He cannot be pleased with the victim.  No way of escape remained but redemption - the creature must be saved by the substitution of a lamb in its place; or if not redeemed, it must die.

My soul, here is a lesson for thee.  That unclean animal is thyself; thou art justly the property of the Lord who made thee and preserves thee, but thou art so sinful that God will not, cannot, accept thee; and it has come to this, the Lamb of God must stand in thy stead, or thou must die eternally.  

Let all the world know of thy gratitude to that spotless Lamb who has already bled for thee, and so redeemed thee from the fatal curse of the law.  Must it not sometimes have been a question with the Israelite which should die, the ass or the lamb?  Would not the good man pause to estimate and compare? Assuredly there was no comparison between the value of the soul of man and the life of the Lord Jesus, and yet the Lamb dies, and man the ass is spared.

My soul, admire the boundless love of God to thee and others of the human race. Worms are bought with the blood of the Son of the Highest!  Dust and ashes redeemed with a price far above silver and gold!  What a doom had been mine had not plenteous redemption been found!  The breaking of the neck of the ass was but a momentary penalty, but who shall measure the wrath to come to which no  limit can be imagined?  Inestimably dear is the glorious Lamb who has redeemed us from such a doom.