A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
deu 16:1THE FEAST OF THE PASSOVER. (Deu. 16:1-22)
Observe the month of Abib--or first-fruits. It comprehended the latter part of our March and the beginning of April. Green ears of the barley, which were then full, were offered as first-fruits, on the second day of the passover.
for in the month of Abib the Lord thy God brought thee out of Egypt by night--This statement is apparently at variance with the prohibition (Exo 12:22) as well as with the recorded fact that their departure took place in the morning (Exo 13:3; Num 33:3). But it is susceptible of easy reconciliation. Pharaoh's permission, the first step of emancipation, was extorted during the night, the preparations for departure commenced, the rendezvous at Rameses made, and the march entered on in the morning.
deu 16:2Thou shalt therefore sacrifice the passover--not the paschal lamb, which was strictly and properly the passover. The whole solemnity is here meant, as is evident from the mention of the additional victims that required to be offered on the subsequent days of the feast (Num 28:18-19; Ch2 35:8-9), and from the allusion to the continued use of unleavened bread for seven days, whereas the passover itself was to be eaten at once. The words before us are equivalent to "thou shalt observe the feast of the passover."
deu 16:3seven days shalt thou eat unleavened bread--a sour, unpleasant, unwholesome kind of bread, designed to be a memorial of their Egyptian misery and of the haste with which they departed, not allowing time for their morning dough to ferment.
deu 16:5Thou mayest not sacrifice the passover within any of thy gates--The passover was to be observed nowhere but in the court of the tabernacle or temple, as it was not a religious feast or sacramental occasion merely, but an actual sacrifice (Exo 12:27; Exo 23:18; Exo 34:25). The blood had to be sprinkled on the altar and in the place where the true Passover was afterwards to be sacrificed for us "at even, at the going down of the sun"--literally, "between the evenings."
deu 16:6at the season--that is, the month and day, though not perhaps the precise hour. The immense number of victims that had to be immolated on the eve of the passover--that is, within a space of four hours--has appeared to some writers a great difficulty. But the large number of officiating priests, their dexterity and skill in the preparation of the sacrifices, the wide range of the court, the extraordinary dimensions of the altar of burnt offering and orderly method of conducting the solemn ceremonial, rendered it easy to do that in a few hours, which would otherwise have required as many days.
deu 16:7thou shalt roast and eat it--(See on Exo 12:8; compare Ch2 35:13).
thou shalt turn in the morning, and go unto thy tents--The sense of this passage, on the first glance of the words, seems to point to the morning after the first day--the passover eve. Perhaps, however, the divinely appointed duration of this feast, the solemn character and important object, the journey of the people from the distant parts of the land to be present, and the recorded examples of their continuing all the time (Ch2 30:21 Ch2 35:17), (though these may be considered extraordinary, and therefore exceptional occasions), may warrant the conclusion that the leave given to the people to return home was to be on the morning after the completion of the seven days.
deu 16:9Seven weeks shalt thou number--The feast of weeks, or a WEEK OF WEEKS: the feast of pentecost (see on Lev 23:10; also see Exo 34:22; Act 2:1). As on the second day of the passover a sheaf of new barley, reaped on purpose, was offered, so on the second day of pentecost a sheaf of new wheat was presented as first-fruits (Exo 23:16; Num 28:26), a freewill, spontaneous tribute of gratitude to God for His temporal bounties. This feast was instituted in memory of the giving of the law, that spiritual food by which man's soul is nourished (Deu 8:3).
deu 16:13Thou shalt observe the feast of tabernacles seven days--(See on Exo 23:14; Lev 23:34; Num 29:12). Various conjectures have been formed to account for the appointment of this feast at the conclusion of the whole harvest. Some imagine that it was designed to remind the Israelites of the time when they had no cornfields to reap but were daily supplied with manna; others think that it suited the convenience of the people better than any other period of the year for dwelling in booths; others that it was the time of Moses' second descent from the mount; while a fourth class are of opinion that this feast was fixed to the time of the year when the Word was made flesh and dwelt--literally, "tabernacled"--among us (Joh 1:14), Christ being actually born at that season.
deu 16:15in all the works of thine hands . . . rejoice--that is, praising God with a warm and elevated heart. According to Jewish tradition, no marriages were allowed to be celebrated during these great festivals, that no personal or private rejoicings might be mingled with the demonstrations of public and national gladness.
deu 16:16Three times in a year shall all thy males appear before the Lord thy God--No command was laid on women to undertake the journeys, partly from regard to the natural weakness of their sex, and partly to their domestic cares.
deu 16:18Judges and officers shalt thou make--These last meant heralds or bailiffs, employed in executing the sentence of their superiors.
in all thy gates--The gate was the place of public resort among the Israelites and other Eastern people, where business was transacted and causes decided. The Ottoman Porte derived its name from the administration of justice at its gates.
deu 16:21Thou shalt not plant thee a grove--A grove has in Scripture a variety of significations--a group of overshadowing trees, or a grove adorned with altars dedicated to a particular deity, or a wooden image in a grove (Jdg 6:25; Kg2 23:4-6). They might be placed near the earthen and temporary altars erected in the wilderness, but they could not exist either at the tabernacle or temples. They were places, which, with their usual accompaniments, presented strong allurements to idolatry; and therefore the Israelites were prohibited from planting them.
deu 16:22Neither shalt thou set thee up any image--erroneously rendered so for "pillar"; pillars of various kinds, and materials of wood or stone were erected in the neighborhood of altars. Sometimes they were conical or oblong, at other times they served as pedestals for the statues of idols. A superstitious reverence was attached to them, and hence they were forbidden.