According to all the rites of it - See all those rites and ceremonies largely explained in the notes on Exodus 12 (note).

In the fourteenth day of this month,.... The first month, the month Nisan or Abib, answering to part of our March:

at even ye shall keep it, in his appointed season: between the two evenings, Exodus 12:6; and even if it fall on the sabbath day, as Jarchi; and this was a sabbath day, according to the Jewish writers (y):

according to all the rites of it, and according to all the ceremonies thereof shall ye keep it; the former of these, according to Jarchi, respects the lamb, and the requisites of it, that it should be without blemish, a male, and of the first year; and the latter, according to him and others, the removal of the leaven, and the seven days of unleavened bread, and the eating of the lamb with bitter herbs: they take in no doubt all that were prescribed by the original law, except the sprinkling of the blood on the doorposts, and also eating the passover in haste, with their loins girt, and shoes on their feet, and staves in their hands; though some think these latter might be observed at this time, when they were unsettled.

(y) Seder Olam Rabba. c. 7.

In the fourteenth day of this month, at even, ye shall keep it in his appointed season: according to {a} all the rites of it, and according to all the ceremonies thereof, shall ye keep it.

(a) Even in all points as the Lord has instituted it.

at even: Heb. between the two evenings

9:1-14 God gave particular orders for the keeping of this passover, and, for aught that appears, after this, they kept no passover till they came to Canaan, Jos 5:10. It early showed that the ceremonial institutions were not to continue always, as so soon after they were appointed, some were suffered to sleep for many years. But the ordinance of the Lord's Supper was not thus set aside in the first days of the Christian church, although those were days of greater difficulty and distress than Israel knew in the wilderness; nay, in the times of persecution, the Lord's Supper was celebrated more frequently than afterward. Israelites in the wilderness could not forget the deliverance out of Egypt. There was danger of this when they came to Canaan. Instructions were given concerning those who were ceremonially unclean, when they were to eat the passover. Those whose minds and consciences are defiled by sin, are unfit for communion with God, and cannot partake with comfort of the gospel passover, till they are cleansed by true repentance and faith. Observe with what trouble and concern these men complained that they were kept back from offering to the Lord. It should be a trouble to us, when by any occasion we are kept back from the solemnities of a sabbath or a sacrament. Observe the deliberation of Moses in resolving this case. Ministers must ask counsel of God's mouth, not determine according to their own fancy or affection, but according to the word of God to the best of their knowledge. And if, in difficult cases, time is taken to spread the matter before God by humble, believing prayer, the Holy Spirit assuredly will direct in the good and right way. God gave directions in this case, and in other similar cases, explanatory of the law of the passover. As those who, against their minds, are forced to absent themselves from God's ordinances, may expect the favours of God's grace under their affliction, so those who, of choice, absent themselves, may expect God's wrath for their sin. Be not deceived: God is not mocked.