Judah was his sanctuary - His home; his abode; his sacred dwelling-place. Judah was the principal or leading tribe, recognized as the tribe where power was to be concentrated, and from which the Messiah was to proceed Genesis 49:8-12; and hence, the name was early used to denote the entire people, and ultimately, as modified in the word Jews, became the common name of the nation.
And Israel his dominion - The nation that he ruled; the nation that had his law; the nation that he governed by his presence - or, of which he was the recognized king. There can be no doubt that the reference here is to God, but it is remarkable that the name "God" is not used. Perhaps the reason may be that this psalm was designed to be employed in connection with the preceding one, and as that consists entirely of the praises of God, it was not necessary to repeat the name when his praise was to be continued under another form, and in connection with another line of thought.

Judah was his sanctuary - He set up his true worship among the Jews, and took them for his peculiar people.
And Israel his dominion - These words are a proof, were there none other, that this Psalm was composed after the days of David, and after the division of the tribes, for then the distinction of Israel and Judah took place.

Judah was his (b) sanctuary, [and] Israel his dominion.
(b) The whole people were witnesses to his holy majesty in adopting them, and of his mighty power in delivering them.

Judah was his sanctuary,.... Meaning not the tribe of Judah only, though that in many things had the preeminence; the kingdom belonging to it, the chief ruler being out of it, especially the Messiah; its standard was pitched and moved first; it offered first to the service of the Lord; and the Jews have a tradition, mentioned by Jarchi and Kimchi, that this tribe, with its prince at the head of it, went into the Red sea first; the others fearing, but afterwards followed, encouraged by their example: but rather all the tribes are meant, the whole body of the people; for this is not to be understood of the tabernacle or temple in the tribe of Judah, sometimes called a sanctuary; for neither of these were in being when Israel came out of Egypt; but it may be rendered, "Judah was his holiness" (u), or was holiness to the Lord, the Lord's holy people; see Jeremiah 2:2, not all internally holy; for there were many that came out of Egypt that were unholy, rebellious, and disobedient, and whose carcasses fell in the wilderness; but externally, when brought out of Egypt they were separated from all other people, and in this sense sanctified, and became a holy and special people, chosen by the Lord to be so; with whom, he made a covenant, and to whom he gave holy laws and righteous statutes: and in this they were typical of those who are effectually called by grace with an holy calling, and unto holiness; have principles of grace and holiness wrought in them, and have Holiness to the Lord written upon them; they have the sanctification of the Spirit, and Christ is made sanctification to them; and they are the Lord's sanctuary, in which he dwells.
And Israel his dominion: for, though all the world is his kingdom and his government, yet the people of Israel were in a very particular and remarkable manner his dominion; from the time of their coming out of Egypt to their having a king, their government was properly a theocracy; God was their King, and by him they were immediately ruled and governed, and had a body of laws given them from him, and were under his immediate care and protection, Exodus 19:5. In this they were typical of the saints called by grace, who are then translated from the power of Satan into the kingdom of Christ; whom they acknowledge to be their Lord and King, and whose laws, commands, and ordinances, they willingly observe; the people of God are often represented as a kingdom, and Christ as King of saints; the Targum is
"the congregation of the house of Judah was united to his holiness, and Israel to his power.''
(u) "sanctificatio ejus", Pagninus, Vatablus; "sanctitas ejus", Gejerus, Michaelis.

Judah - Or Israel, one tribe being put for all. Judah he mentions as the chief of all the tribes.