I had to do some digging to understand what appeared to be a contradiction. Do you need to offer an acceptable animal to God, or is there a loophole?
What I came to realize is that this chapter is not about offering sacrifices for sin. Those animals had to be perfect, without defect or God would not forgive sin. Leviticus 27 is talking about something else all together.
What we see here are offerings to God that accompany a vow to serve Him. Matthew Henry gave the example of people wanting to sweep the tabernacle or run errands for the priests. (Matthew Henry’s Commentary in One Volume; Zondervan Publishing House; 1961; page 141) These willing servants would pay for the privilege of serving, rather than expecting payment for their services.
So God gave them guidelines. The offerings were not sin sacrifices, yet the offerings still needed to be worthy of God. “Good animals” rather than “bad animals;” a fair price for a man willing to serve or the price of a house or land of the person willing to serve.
It costs to serve God. Don’t think it doesn’t.
Now, if a willing servant had only a “bad animal” it did not mean he couldn’t serve. But that “bad animal” would not be acceptable to God. In that case, the servant could bring what they had and exchange the inferior animal for a “good animal,” and offer that to God.
But that didn’t mean he could take his “bad animal” home. Both animals were accepted as the offering, and neither could be bought back.
God didn’t lower the standard because all the guy had was a “bad animal.” God didn’t say, “Well, your heart is in the right place. You had good intentions. That’s good enough.”
It wasn’t good enough. God’s requirement for this offering was a “good animal.” Period.
If the willing servant could have exchanged his inferior animal for the proper one, then taken his inferior animal home, it would have cost him nothing to serve God. And it always costs to serve God.
In fact, in this case the cost of serving God was now TWO animals instead of one. The cost went up. Warren Wiersbe talks about the cost of making rash promises to God. Those can be very costly. (With The Word; Oliver Nelson Publishing; 1991; page 84).
Do you remember the young man who told Jesus he wanted to follow Him? (see Matthew 19, Mark 10, Luke 18). I believe he meant it, until he heard Jesus tell him the cost of following Him:
The young man, though willing, could not bring himself to pay the price when it came right down to it.
I hope you’ve determined to follow Jesus. But don’t get caught up in emotion and make a promise you can’t keep. Count the cost. Because, just as God keeps His promises to us, He expects us to keep our promises to Him.