Leviticus 12:8

8 And if she cannot afford a lamb, then shall she take two turtle-doves or two young pigeons, one for a whole-burnt-offering, and one for a sin-offering; and the priest shall make atonement for her, and she shall be purified.

Leviticus 12:8 Meaning and Commentary

Leviticus 12:8

And if she be not able to bring a lamb
As everyone was not in circumstances sufficient to be at the expense of buying a lamb for this purpose, having none of their own:

then she shall bring two turtles, or two young pigeons;
which was a kind and merciful provision for the poorer sort; since it was necessary that by them the favour received should be acknowledged, as well as the sin attending them in such circumstances should be atoned for. This being the offering brought by the mother of our Lord, shows the state of poverty in which she was; and by this, and the circumcision of her child, and the presentation of it before the Lord at the time of her purification, it appears that they were both under the law, and obedient to it:

the one for a burnt offering, and the other for a sin [offering];
Jarchi observes, that in oblations the sin offering goes before the burnt offering, for sin being atoned for, the gift was accepted; but here the burnt offering went first, the reason is not very apparent:

and the priest shall make an atonement for her, and she shall be
clean;
equally the same as if she had brought a lamb, instead of young pigeons, or turtledoves.

Leviticus 12:8 In-Context

6 And when the days of her purification shall have been fulfilled for a son or a daughter, she shall bring a lamb of a year old without blemish for a whole-burnt-offering, and a young pigeon or turtle-dove for a sin-offering to the door of the tabernacle of witness, to the priest.
7 And he shall present it before the Lord, and the priest shall make atonement for her, and shall purge her from the fountain of her blood; this is the law of her who bears a male or a female.
8 And if she cannot afford a lamb, then shall she take two turtle-doves or two young pigeons, one for a whole-burnt-offering, and one for a sin-offering; and the priest shall make atonement for her, and she shall be purified.

The Brenton translation of the Septuagint is in the public domain.