And if she be not able to bring a lamb, then she shall bring two turtles, or two young pigeons - As the Virgin Mary brought only the latter, hence it is evident that she was not able, i. e., she was not rich enough to provide the former; for such a holy woman would not have brought the less offering had she been capable of bringing the greater. How astonishing is this! The only heir to the throne of David was not able to bring a lamb to offer in sacrifice to God! How abominable must sin be when it required him who was in the form of God thus to empty and to humble himself, yea, even to the death of the cross, in order to make an atonement for it, and to purify the soul from all defilement!

The priest shall make an atonement for her - Every act of man is sinful, but such as proceed from the influence of the grace and mercy of God. Her sorrow in conception, and her pain in bringing forth children, reminded the woman of her original offense; an offense which deserved death, an offense which she could not expiate, and for which a sacrifice must be offered: and in reference to better things the life of an animal must be offered as a ransom for her life. And being saved in childbed, though she deserved to die, she is required, as soon as the days of her separation were ended, to bring a sacrifice according to her ability to the priest, that he might offer it to God as an atonement for her. Thus, wherever God keeps up the remembrance of sin, he keeps up also the memorial of sacrifice, to show that the state of a sinner, howsoever deplorable, is not hopeless, for that he himself has found out a ransom. Every where, in the law and in the Gospel, in every ordinance and in every ceremony, we may see both the justice and the mercy of God. Hence, while we have the knowledge of our sin we have also the knowledge of our cure. Reader, whilst thou art confessing thy own misery do not forget the Lord's mercy; and remember, be saves to the uttermost all that come through Christ unto him.

she be not able to bring a lamb. [heb] her hand find not sufficiency of a lamb

Leviticus 1:14 And if the burnt sacrifice for his offering to the LORD be of fowls, then he shall bring his offering of turtledoves...

Leviticus 5:7 And if he be not able to bring a lamb, then he shall bring for his trespass, which he has committed, two turtledoves...

Leviticus 14:22 And two turtledoves, or two young pigeons, such as he is able to get; and the one shall be a sin offering...

Leviticus 15:14,29 And on the eighth day he shall take to him two turtledoves, or two young pigeons...

Luke 2:22,24 And when the days of her purification according to the law of Moses were accomplished, they brought him to Jerusalem...

2 Corinthians 8:9 For you know the grace of our Lord Jesus Christ, that, though he was rich, yet for your sakes he became poor...

make an atonement

Leviticus 4:26 And he shall burn all his fat on the altar, as the fat of the sacrifice of peace offerings...

When burn offerings and sin offerings were brought together, the sin offerings were first offered.

The Early Years of Jesus
Matt. i. 1 to ii. 23; Luke i. 5 to ii. 52; iii. 23-38 58. It is surprising that within a century of the life of the apostles, Christian imagination could have so completely mistaken the real greatness of Jesus as to let its thirst for wonder fill his early years with scenes in which his conduct is as unlovely as it is shocking. That he who in manhood was "holy, harmless, undefiled, separate from sinners" (Heb. vii. 26), could in youth, in a fit of ill-temper, strike a companion with death and then …
Rush Rhees—The Life of Jesus of Nazareth