And he shall bring them unto the priest
Either two turtledoves, or two young pigeons:
who shall offer [that] which [is] for the sin [offering] first;
that which is chosen for it, as the Targum of Jonathan; and this choice was made, not by the priest, but by the man that brought the offering, who separated it, and said, lo, this is a sin offering, and after that said, lo, this is a burnt offering F1; the sin offering was offered first, which was to make atonement for sin, and then the burnt offering, to denote the divine acceptance of it; and so Ben Gersom observes, it was proper to offer the sin offering first, to atone for his sin, that after he (God) was appeased this way, he might receive his gift; for the burnt offering was as a gift. Jarchi compares it to an advocate, who first goes in to appease, and when he has appeased, the gift goes in after him:
and wring off his head from his neck, but shall not divide it
be it a turtledove or a young pigeon, so it was to be served; the head was not to be separated from the body, but was nipped by the nail of the priest "in" the neck, as it might be rendered F2; over against the neck, as the Targums of Onkelos and Jonathan render it; the hinder part, or what is behind the throat, as Jarchi and Ben Molech interpret it; so that the part which was nipped was the neck; and this nip was made so large, as that the blood was let out by it, as appears from the following verse ( Leviticus 5:9 ) , and yet the head was not divided from the body; the head hung by a piece of skin on the back part; of the manner of performing this, and the mystery of it, (See Gill on Leviticus 1:15).