(1) His foundation.—This abrupt commencement with a clause without a verb has led to the conjecture that a line has dropped away. But this is unnecessary if we neglect the accents, and take gates of Zion in apposition with His foundation:
His foundation on the holy hill
Loveth Jehovah, (even) Zion’s gates,
More than all Jacob’s dwellings.
Here His foundation is equivalent to that which He hath founded, and the gates are put by metonymy for the city itself. (Comp. Jeremiah 14:2.)
With regard to the plural, mountains, it is probably only poetical, though geographically it is correct to speak of Jerusalem as situated on hills. Dean Stanley speaks of “the multiplicity of the eminences” which the city “shares, though in a smaller compass, with Rome and Constantinople” (Sinai and Palestine, p. 177).

(3) The meaning of this verse is obvious in spite of its many grammatical difficulties. The praise of Zion had found many tongues, but the poet implies that he is going to swell the chorus.

(4) This verse may be paraphrased—
I will mention to my intimates Rahab and Babylon; (I will say) look at Philistia and Tyre—yes, and even Ethiopia. So-and-so was born there.
The last clause is literally this was born there, and on its reference the whole meaning of the verse and the whole intention of the psalm turn. Now immediately after the mention of a place, there must surely refer to that place, and not to a place mentioned in the previous verse and there too addressed as in the second person. The demonstrative this, is evidently used in a general way. (Comp. the fuller form, Judges 18:4, &c.) The poet begins his special addition to the praises of Zion, by enumerating various renowned nations much in the same way as Horace’s
“Laudabunt alii claram Rhodon, aut Mitylenen.”
only instead of leaving them as a theme to others he tells us what he himself in ordinary conversation might say of these places, and of the estimation in which their natives were held. It is hardly possible to escape from the conclusion that the Palestinian Jew is here implying his superiority to those of his race who were born abroad, a spirit shown so strongly in the relations of the Hebrews to the Hellenistic Jews in the New Testament.
Rahab undoubtedly stands for Egypt, but the exact origin of the term and of its connection with Egypt is much disputed. Most probably it is a term (possibly Coptic) for some large sea or river monster symbolic of Egypt. (Comp. the word “dragons,” Psalms 74:13, and see Job 9:13; Job 26:12.)
Ethiopia—Heb., Khûsh (in Authorised Version Cush). (See Genesis 10:6 : 2 Kings 19:9.)
There is no need with our explanation to look for emblematic reasons for the choice of names in this verse—as Egypt for antiquity; Babylon, strength; Tyre, wealth, &c. There is no one of the districts where Jews of the Dispersion might not have been found, but no doubt in his enumeration the poet takes care to mention countries near and far, as Philistia and Ethiopia. There appears, however, to have been a district in Babylonia known to the Hebrews as Khûsh (Lenormant, Origines de l’Histoire; and see a paper on the site of Eden, in the Nineteenth Century for October, 1882). The parallelism would be improved by this reference here.

(5) And of Zion . . .—This verse must be taken as antithetical to the preceding. The poet claims a prouder boast for natives of Jerusalem, because it was established by the Most High. Render, But of Zion it is said, “This man and that (literally, man and man) was born in her, and her the Most High established.”

(6) The proud boast of the preceding verse is repeated here with allusion to the census or birth-register of citizens. (See Ezekiel 13:9; Isaiah 4:3; Psalms 69:28, Note.) No doubt these lists were often produced or appealed to in triumph to mark the superiority of a native of Jerusalem over those born at a distance.

(7) The literal sense of this most obscure verse is—
“And singers as trumpeters
All my springs in Thee,
which we may paraphrase, keeping in the same line with the rest of the psalm, For such an one (celebrating his birthday, Genesis 40:20, Matthew 14:6) the singers and musicians will sing (to Zion), “All my offspring is in Thee.” Not only is it a boast to have been born in Zion, but in the genuine Hebrew spirit the boast is continued into the future generations, and the Hebrew of the Hebrews exults in addressing the sacred city as the cradle of his family.
For this figurative application of the word “springs” to posterity, comp. Psalms 68:26; Isaiah 48:1; Proverbs 5:16.