Now an omer is the tenth part of an ephah - About six pints, English. See Clarke's note on Exodus 16:16. The true place of this verse seems to be immediately after Exodus 16:18, for here it has no connection.
1. On the miracle of the manna, which is the chief subject in this chapter, a good deal has already been said in the preceding notes. The sacred historian has given us the most circumstantial proofs that it was a supernatural and miraculous supply; that nothing of the kind had ever been seen before, and probably nothing like it had ever afterwards appeared. That it was a type of our blessed Redeemer, and of the salvation which he has provided for man, there can be no doubt, for in this way it is applied by Christ himself; and from it we may gather this general conclusion, that salvation is of the Lord. The Israelites must have perished in the wilderness, had not God fed them with bread from heaven; and every human soul must have perished, had not Jesus Christ come down from heaven, and given himself for the life of the world.
2. God would have the Israelites continually dependent on himself for all their supplies; but he would make them, in a certain way, workers with him. He provided the manna; they gathered and ate it. The first was God's work; the latter, their own. They could not produce the manna, and God would not gather it for them. Thus the providence of God appears in such a way as to secure the co-operation of man. Though man should plant and water, yet it is God who giveth the increase. But if man neither plant nor water, God will give no increase. We cannot do God's work, and he will not do ours. Let us, therefore, both in things spiritual and temporal, be workers together with Him.
3. This daily supply of the manna probably gave rise to that petition, Give us to-day our daily bread. It is worthy of remark, 1. That what was left over night contrary to the command of God bred worms and stank; 2. That a double portion was gathered on the day preceding the Sabbath; 3. That this alone continued wholesome on the following day; and, 4. That none fell on the Sabbath! Hence we find that the Sabbath was considered a Divine institution previously to the giving of the Mosaic law; and that God continued to honor that day by permitting no manna to fall during its course. Whatever is earned on the Sabbath is a curse in a man's property. They who Will be rich, fall into temptation and into a snare, etc.; for, using illicit means to acquire lawful things, they bring God's curse upon themselves, and are drowned in destruction and perdition. Reader, dost thou work on the Sabbath to increase thy property? See thou do it not! Property acquired in this way will be a curse both to thee and to thy posterity.
4. To show their children and children's children what God had done for their fathers, a pot of manna was laid up before the testimony. We should remember our providential and gracious deliverances in such a way as to give God the praise of his own grace. An ungrateful heart is always associated with an unbelieving mind and an unholy life. Like Israel, we should consider with what bread God has fed our fathers, and see that we have the same; the same Christ - the bread of life, the same doctrines, the same ordinances, and the same religious experience. How little are we benefited by being Protestants, if we be not partakers of the Protestant faith! And how useless will even that faith be to us, if we hold the truth in unrighteousness. Our fathers had religion enough to enable them to burn gloriously for the truth of God! Reader, hast thou so much of the life of God in thy soul, that thou couldst burn to ashes at the stake rather than lose it? In a word, couldst thou be a martyr? Or hast thou so little grace to lose, that thy life would be more than an equivalent for thy loss? Where is the manna on which thy fathers fed?

Now an omer [is] the tenth [part] of an (q) ephah.
(q) Which measure contained about five gallons.

Now an omer is the tenth part of an ephah. Frequent mention being made of this measure in the above relation, as containing the quantity of each man's share of the manna daily, during the forty years' stay in the wilderness; an account is given by the historian how much it contained, by which it may appear what a sufficient provision was made: an ephah, according to Jarchi, contained three seahs (or pecks); a scab, six kabs; a kab, four logs; a log, six egg shells; and the tenth part of an ephah was forty three egg shells, and the fifth part of one: but Dr. Cumberland (b) has reduced this to our measure, and has given it more clearly and distinctly; an ephah, according to him, contained, in wine measure, seven gallons, two quarts, and about half a pint; in corn measure, six gallons, three pints, and three solid inches; and an omer three quarts; which being made into bread, must be more than any ordinary man could well eat; for, as Ainsworth observes, an omer was twice as much as the choenix, (a measure mentioned in Revelation 6:6.) which was wont to be a man's allowance of bread corn for a day; and what a vast quantity must fall every day to supply so large a number of people with such a measure; some have reckoned it at 94,466 bushels every day, and that there must be consumed in forty years 1,379,203,600 bushels (c).
(b) Of Scripture Weights and Measures, ch. 3. p. 64, 86, 87. ch. 4. p. 137. (c) Vid. Scheuchzer. Physic. Saer. vol. 2. p. 177, 178.

In conclusion, the quantity of the manna collected for the daily supply of each individual, which was preserved in the sanctuary, is given according to the ordinary measurement, viz., the ephah. The common opinion, that עמר was the name for a measure of capacity, which was evidently shared by the Seventy, who have rendered the word γομόρ, has no foundation so far as the Scriptures are concerned. Not only is it a fact, that the word omer is never used as a measure except in this chapter, but the tenth of an ephah is constantly indicated, even in the Pentateuch, by "the tenth part of an ephah" (Leviticus 5:11; Leviticus 6:13; Numbers 5:15; Numbers 28:5), or "a tenth deal" (Exodus 29:40; Leviticus 14:10, etc.; in all 30 times). The omer was a small vessel, cup, or bowl, which formed part of the furniture of every house, and being always of the same size, could be used as a measure in case of need.
(Note: Omer proprie nomen poculi fuit, quale secum gestare solent Orientales, per deserta iter facientes, ad hauriendam si quam rivus vel fons offerret aquam.... Hoc in poculo, alia vasa non habentes, et mannam collegerunt Israelitae (Michaelis, Supplem. ad Lex. hebr., p. 1929). Cf. Hengstenberg, Dissertations on the Pentateuch, vol. ii. p. 172.)
The ephah is given by Bertheau as consisting of 198577 Parisian cubic inches, and holding 739,800 Parisian grains of water; Thenius, however, gives only 101439 Parisian, or 112467 Rhenish inches. (See my Archologie, ii. 141-2.)