The common people - literally, as in the margin, "the people of the land." Compare Leviticus 20:2, Leviticus 20:4; 2-Kings 11:18. It was the ordinary designation of the people, as distinguished from the priests and the rulers.

The common people - עם הארץ am haarets, the people of the land, that is, any individual who was not a priest, king, or ruler among the people; any of the poor or ordinary sort. Any of these, having transgressed through ignorance, was obliged to bring a lamb or a kid, the ceremonies being nearly the same as in the preceding cases. The original may denote the very lowest of the people, the laboring or agricultural classes.
The law relative to the general cases of sins committed through ignorance, and the sacrifices to be offered on such occasions, so amply detailed in this chapter, may be thus recapitulated. For all sins and transgressions of this kind committed by the people, the prince, and the priest, they must offer expiatory offerings. The person so sinning must bring the sacrifice to the door of the tabernacle, and lay his hands upon its head, as in a case already referred to, acknowledging the sacrifice to be his, that he needed it for his transgression; and thus he was considered as confessing his sin, and the sin was considered as transferred to the animal, whose blood was then spilt to make an atonement. See Clarke on Leviticus 1:4 (note). Such institutions as these could not be considered as terminating in themselves, they necessarily had reference to something of infinitely higher moment; in a word, they typified Him whose soul was made an offering for sin, Isaiah 53:10. And taken out of this reference they seem both absurd and irrational. It is obviously in reference to these innocent creatures being brought as sin-offerings to God for the guilty that St. Paul alludes 2-Corinthians 5:21, where he says, He (God) made him to be sin (ἁμαρτιαν, a sin-offering) for us Who Knew No Sin, that we might be made the righteousness of God - holy and pure by the power and grace of God, in or through him. And it is worthy of remark, that the Greek word used by the apostle is the same by which the Septuagint, in more than fourscore places in the Pentateuch, translate the Hebrew word הטאה hattaah, sin, which in all those places our translation renders sin-offering. Even sins of ignorance cannot be unnoticed by a strict and holy law; these also need the great atonement: on which account we should often pray with David, Cleanse thou me from secret faults! Psalm 19:12. How little attention is paid to this solemn subject! Sins of this kind - sins committed sometimes ignorantly, and more frequently heedlessly, are permitted to accumulate in their number, and consequently in their guilt; and from this very circumstance we may often account for those painful desertions, as they are called, under which many comparatively good people labor. They have committed sins of ignorance or heedlessness, and have not offered the sacrifice which can alone avail in their behalf. How necessary in ten thousand cases is the following excellent prayer! "That it may please thee to give us true repentance; to forgive us all our sins, negligences, and ignorances; and to endue us with the grace of thy Holy Spirit, to amend our lives according to thy Holy Word." - Litany.

And if anyone of the common people sin through ignorance,.... Or, "if one soul of the people of the earth": that is, a single person, and so is distinguished from the congregation, one of the common sort of people; however is neither an high priest, nor a prince, or king, but either a common priest, or Levite, or Israelite; no man is free from sin; all sorts of persons, of all ranks and degrees, high and low, rich and poor, men in office, civil or ecclesiastical, or in whatsoever state of life, are liable to sin, and do sin continually, either ignorantly or willingly; and Christ is a sacrifice for all sins and for all sorts of sinners:
whilst he doeth somewhat; &c. See Gill on Leviticus 4:2, Leviticus 4:13, Leviticus 4:22.

Here is the law of the sin-offering for a common person. To be able to plead, when charged with sin, that we did it ignorantly, and through the surprise of temptation, will not bring us off, if we have no interest in that great plea, Christ hath died. The sins of ignorance committed by a common person, needed a sacrifice; the greatest are not above, the meanest are not below Divine justice. None, if offenders, were overlooked. Here rich and poor meet together; they are alike sinners, and welcome to Christ. From all these laws concerning the sin-offerings, we may learn to hate sin, and to watch against it; and to value Christ, the great and true Sin-offering, whose blood cleanses from all sin, which it was not possible that the blood of bulls and of goats should take away. For us to err, with the Bible in our hands, is the effect of pride, sloth, and carelessness. We need to use frequent self-examination, with serious study of the Scriptures, and earnest prayer for the convincing influences of God the Holy Spirit; that we may detect our sins of ignorance, repent, and obtain forgiveness through the blood of Christ.

if any one of the common people sin through ignorance--In this case the expiatory offering appointed was a female kid, or a ewe-lamb without blemish; and the ceremonies were exactly the same as those observed in the case of the offending ruler [Leviticus 4:22-26]. In these two latter instances, the blood of the sin offering was applied to the altar of burnt offering--the place where bloody sacrifices were appointed to be immolated. But the transgression of a high priest, or of the whole congregation, entailing a general taint on the ritual of the tabernacle, and vitiating its services, required a further expiation; and therefore, in these cases, the blood of the sin offering was applied to the altar of incense [Leviticus 4:6, Leviticus 4:17].

In the case of the sin of a common Israelite ("of the people of the land," i.e., of the rural population, Genesis 23:7), that is to say, of an Israelite belonging to the people, as distinguished from the chiefs who ruled over the people (2-Kings 11:18-19; 2-Kings 16:15), the sin-offering was to consist of a shaggy she-goat without blemish, or a ewe-sheep (Leviticus 4:32). The ceremonial in both cases was the same as with the he-goat (Leviticus 4:23.). - "According to the offerings made by fire unto the Lord" (Leviticus 4:35): see at Leviticus 3:5.