Sifrei Mitzvot sobre Levítico 15:14

That a man having an issue shall bring a sacrifice, after he is cleansed of his issue, as it is said, “And when he that hath an issue is cleansed of his issue….” (Lev. 15:13-15).

The commandment of the sacrifice of the zav when he is healed from his discharge: That the zav offer his sacrifice after he is healed from his discharge, as it is stated (Leviticus 16:13-14), “When the zav is purified from his discharge, etc. And on the eighth day, he shall take two doves, etc.” And this sacrifice is two doves or two young pigeons — one for a sin-offering and one for a burnt-offering. And he is called, “lacking atonement,” until he offers it.

That which I have written above (Sefer HaChinukh 95), that the matter of the sacrifice is to hint to the lowering of the impulse of the desiring body and raise up the intellectual soul, is from the roots of the commandment. And hence when the zav is healed, it is fitting for him to recognize the evil of his desire and to straighten out his body with all of his strength. And with the matter of the sacrifice, he will begin to take instruction.