Here is, I. A law against deceitful weights and measures: they must not only not use them, but they must not have them, not have them in the bag, not have them in the house (Deu 25:13, Deu 25:14); for, if they had them, they would be strongly tempted to use them. They must not have a great weight and measure to buy by and a small one to sell by, for that was to cheat both ways, when either was bad enough; as we read of those that made the ephah small, in which they measured the corn they sold, and the shekel great, by which they weighed the money they received for it, Amo 8:5. But thou shalt have a perfect and just weight, v. 15. That which is the rule of justice must itself be just; if that be otherwise, it is a constant cheat. This had been taken care of before, Lev 19:35, Lev 19:36. This law is enforced with two very good reasons: - 1. That justice and equity will bring down upon us the blessing of God. The way to have our days lengthened, and to prosper, is to be just and fair in all our dealings Honesty is the best policy. 2. That fraud and injustice will expose us to the curse of God, Deu 25:16. Not only unrighteousness itself, but all that do unrighteously, are an abomination to the Lord. And miserable is that man who is abhorred by his Maker. How hateful, particularly, all the arts of deceit are to God, Solomon several times observes, Pro 11:1; Pro 20:10, Pro 20:23; and the apostle tells us that the Lord is the avenger of all such as overreach and defraud in any matter, Th1 4:6.

II.A law for the rooting out of Amalek. Here is a just weight and a just measure, that, as Amalek had measured to Israel, so it should be measure to Amalek again.

1.The mischief Amalek did to Israel must be here remembered, Deu 25:17, Deu 25:18. When it was first done it was ordered to be recorded (Exo 17:14-16), and here the remembrance of it is ordered to be preserved, not in personal revenge (for that generation which suffered by the Amalekites was gone, so that those who now lived, and their posterity, could not have any personal resentment of the injury), but in a zeal for the glory of God (which was insulted by the Amalekites), that throne of the Lord against which the hand of Amalek was stretched out. The carriage of the Amalekites towards Israel is here represented, (1.) As very base and disingenuous. They had no occasion at all to quarrel with Israel, nor did they give them any notice, by a manifesto or declaration of war; but took them at an advantage, when they had just come out of the house of bondage, and, for aught that appeared to them, were only going to sacrifice to God in the wilderness. (2.) As very barbarous and cruel; for they smote those that were more feeble, whom they should have succoured. The greatest cowards are commonly the most cruel; while those that have the courage of a man will have the compassion of a man. (3.) As very impious and profane: they feared not God. If they had had any reverence for the majesty of the God of Israel, which they saw a token of in the cloud, or any dread of his wrath, which they lately heard of the power of over Pharaoh, they durst not have made this assault upon Israel. Well, here was the ground of the quarrel: and it shows how God takes what is done against his people as done against himself, and that he will particularly reckon with those that discourage and hinder young beginners in religion, that (as Satan's agents) set upon the weak and feeble, either to divert them or to disquiet them, and offend his little ones.

2.This mischief must in due time be revenged, Deu 25:19. When their wars were finished, by which they were to settle their kingdom and enlarge their coast, then they must make war upon Amalek (Deu 25:19), not merely to chase them, but to consume them, to blot out the remembrance of Amalek. It was an instance of God's patience that he deferred the vengeance so long, which should have led the Amalekites to repentance; yet an instance of fearful retribution that the posterity of Amalek, so long after, were destroyed for the mischief done by their ancestors to the Israel of God, that all the world might see, and say, that he who toucheth them toucheth the apple of his eye. It was nearly 400 years after this that Saul was ordered to put this sentence in execution (1 Sa. 15), and was rejected of God because he did not do it effectually, but spared some of that devoted nation, in contempt, not only of the particular orders he received from Samuel, but of this general command here given by Moses, which he could not be ignorant of. David afterwards made some destruction of them; and the Simeonites, in Hezekiah's time, smote the rest that remained (Ch1 4:43); for when God judges he will overcome.

But thou shall have a perfect and just weight, a perfect and just measure shall thou have,.... That is, full weights, and full measures; and such as are alike, and everywhere used, according to the standard of the country; See Gill on Lev 19:36,

that thy days may be lengthened in the land which the Lord thy God giveth thee; long life was always reckoned a blessing, and is frequently promised to, obedience, and particularly long life in the land of Canaan; which was a most delightful and fruitful land, and which a man might wish to live long in; deceitful men, are threatened with not living half their days, and such may they be said to be that use false weights and measures, Psa 55:23.

Thou shalt not have . . . divers weights--Weights were anciently made of stone and are frequently used still by Eastern shopkeepers and traders, who take them out of the bag and put them in the balance. The man who is not cheated by the trader and his bag of divers weights must be blessed with more acuteness than most of his fellows [ROBERTS]. (Compare Pro 16:11; Pro 20:10).