Adam Clarke on Leviticus 14:21

And if he be poor - he shall take one lamb - There could be no cleansing without a sacrifice. On this ground the apostle has properly observed that all things under the law are purged with blood; and that without shedding of blood there is no remission. Even if the person be poor, he must provide one lamb; this could not be dispensed with: - so every soul to whom the word of Divine revelation comes, must bring that Lamb of God which takes away the sin of the world. There is no redemption but in his blood.