For this is a statute to Israel. To give the more effect to the preceding exhortation, it is here taught that this law or ordinance had been prescribed to God's ancient people, for the purpose of ratifying the everlasting covenant. And as in covenants there is a mutual agreement between the parties, it is declared that this statute was given to Israel, and that God, in contracting, reserved this for himself, as a right to which he was justly entitled.

For this was a statute for Israel - See Exodus 12:3. That is, it was a law for the whole Jewish people, for all who had the name Israel, for all the descendants of Jacob. The word was is not in the original, as if this had been an old commandment which might now be obsolete, but the idea is one of perpetuity: it is a perpetual law for the Hebrew people.
A law of the God of Jacob - Hebrew, a judgment; or, right. The idea is, that it was what was due to God; what was his right. It was a solemn claim that he should be thus acknowledged. It was not a matter of conventional arrangement, or a matter of convenience to them; nor was it to be observed merely because it was found to be expedient and conducive to the welfare of the nation. It was a matter of right and of claim on the part of God, and was so to be regarded by the nation. The same is true now of the Sabbath, and of all the appointments which God has made for keeping up religion in the world. All these arrangements are indeed expedient and proper; they conduce to the public welfare and to the happiness of man; but there is a higher reason for their observance than this. It is that God demands their observance; that he claims as his own the time so appropriated. Thus he claims the Sabbath, the entire Sabbath, as his own; he requires that it shall be employed in his service, that it shall be regarded as his day; that it shall be made instrumental in keeping up the knowledge of himself in the world, and in promoting his glory. Exodus 20:10. People, therefore, "rob God" (compare Malachi 3:8) when they take this time for needless secular purposes, or devote it to other ends and uses. Nor can this be sinless. The highest guilt which man can commit is to "rob" his Maker of what belongs to Him, and of what He claims.

This was a statute for Israel - See the statute, Numbers 10:10 (note), and Leviticus 23:24 (note).

For this was a statute for Israel,.... It was not a piece of will worship, or device of the children of Israel, but was of divine institution; that the passover should be kept at the time it was; and that the trumpets should be blown on the new moon, or first of Tisri; and that the feast of tabernacles should be kept on the fifteenth of the same month:
and a law of the God of Jacob; and therefore to be observed by Jacob's posterity: the law for the one is in Exodus 12:18 and for the other is in Leviticus 23:24 and so all the ordinances of Christ, and of the Gospel dispensation, are to be regarded on the same account, because they are the statutes and appointments of God; and the feast of tabernacles is particularly put for them all, Zac 14:16.

Psalm 81:4-5 now tell whence the feast which is to be met with singing and music has acquired such a high significance: it is a divine institution coming from the time of the redemption by the hand of Moses. It is called חק as being a legally sanctioned decree, משׁפּט as being a lawfully binding appointment, and עדוּת as being a positive declaration of the divine will. The ל in לישׂראל characterizes Israel as the receiver, in לאלהי the God of Israel as the owner, i.e., Author and Lawgiver. By בּצעתו the establishing of the statute is dated back to the time of the Exodus; but the statement of the time of its being established, "when He went out over the land of Egypt," cannot be understood of the exodus of the people out of Egypt, natural as this may be here, where Israel has just been called יהוסף (pathetic for יוסף), by a comparison with Genesis 41:45, where Joseph is spoken of in the same words. For this expression does not describe the going forth out of a country, perhaps in the sight of its inhabitants, Numbers 33:3, cf. Exodus 14:8 (Hengstenberg), but the going out over a country. Elohim is the subject, and צאת is to be understood according to Exodus 11:4 (Kimchi, De Dieu, Dathe, Rosenmller, and others): when He went out for judgment over the land of Egypt (cf. Micah 1:3). This statement of the time of itself at once decides the reference of the Psalm to the Passover, which commemorates the sparing of Israel at that time (Exodus 12:27), and which was instituted on that very night of judgment. The accentuation divides the verse correctly. According to this, שׂפת לא־ידעתּי אשׁמע is not a relative clause to מצרים: where I heard a language that I understood not (Psalm 114:1). Certainly ידע שׂפה, "to understand a language," is an expression that is in itself not inadmissible (cf. ידע ספר, to understand writing, to be able to read, Isaiah 29:11.), the selection of which instead of the more customary phrase שׁמע לשׁון (Deuteronomy 28:49; Isaiah 33:19; Jeremiah 5:15) might be easily intelligible here beside אשׁמע; but the omission of the שׁם (אשׁר) is harsh, the thought it here purposeless, and excluded with our way of taking בצאתו. From the speech of God that follows it is evident that the clause is intended to serve as an introduction of this divine speech, whether it now be rendered sermonem quem non novi (cf. Psalm 18:44, populus quem non novi), or alicujus, quem non novi (Ges. 123, rem. 1), both of which are admissible. It is not in some way an introduction to the following speech of God as one which it has been suddenly given to the psalmist to hear: "An unknown language, or the language of one unknown, do I hear?" Thus Dderlein explains it: Subitanea et digna poetico impetu digressio, cum vates sese divino adflatu subito perculsum sentit et oraculum audire sibi persuadet; and in the same way De Wette, Olshausen, Hupfeld, and others. But the oracle of God cannot appear so strange to the Israelitish poet and seer as the spirit-voice to Eliphaz (Job 4:16); and moreover אשׁמע after the foregoing historical predicates has the presumption of the imperfect signification in its favour. Thus, then, it will have to be interpreted according to Exodus 6:2. It was the language of a known, but still also unknown God, which Israel heard in the redemption of that period. It was the God who had been made manifest as יהוה only, so to speak, by way of prelude hitherto, who now appeared at this juncture of the patriarchal history, which had been all along kept in view, in the marvellous and new light of the judgment which was executed upon Egypt, and of the protection, redemption, and election of Israel, as being One hitherto unknown, as the history of salvation actually then, having arrived at Sinai, receives an entirely new form, inasmuch as from this time onwards the congregation or church is a nation, and Jahve the King of a nation, and the bond of union between them a national law educating it for the real, vital salvation that is to come. The words of Jahve that follow are now not the words heard then in the time of the Exodus. The remembrance of the words heard forms only a transition to those that now make themselves heard. For when the poet remembers the language which He who reveals Himself in a manner never before seen and heard of spoke to His people at that time, the Ever-living One Himself, who is yesterday and to-day the same One, speaks in order to remind His people of what He was to them then, and of what He spake to them then.