They have inclosed themselves in their own fat If the translation which is given by others is considered preferable, They have inclosed their own fat, the meaning will be quite the same. Some Jewish interpreters explain the words thus: that being stuffed with fat, and their throat being, as it were, choked with it, they were unable to speak freely; but this is a very meagre and unsatisfactory exposition. By the word fat, I think, is denoted the pride with which they were filled and swollen, as it were, with fatness. It is a very appropriate and expressive metaphor to represent them as having their hearts choked up with pride, in the manner in which corpulent persons are affected from the fat within them. [1] David complains of their being puffed up with their wealth and pleasures, and accordingly we see the ungodly, the more luxuriously they are pampered, conducting themselves the more outrageously and proudly. But I think there is described by the word fat an inward vice namely, their being inclosed on all sides with arrogance and presumption, and their having become utter strangers to every feeling of humanity. [2] The Psalmist next declares that this is abundantly manifested in their language. In short, his meaning is, that inwardly they swell with pride, and that they take no pains to conceal it, as appears from the high swelling words to which they give utterance. When it is said, They have spoken proudly with their mouth, the word mouth is not a pleonasm, as it often is in other places; for David means, that with mouths widely opened they pour forth scornful and contemptuous language, which bears testimony to the pride which dwells within them.

Footnotes

1 - "Comme les gens replets se trouvent saisis de leur graisse au dedans." -- Fr. "The sacred writers employ this term [fat] to signify a body pampered to excess by luxury and self-indulgence, Psalm 73:7; 119:70; Job 15:27." - French and Skinner's Translation of the Book of Psalms. There may no doubt be a reference to the personal appearance and sensual indulgence of David's enemies. But something more is implied. "We know that, in the figurative language of Scripture fatness denotes pride. This connection of ideas is still maintained in the East, where, when it is intended to indicate a proud man, he is said to be fat, or to look fat, whether really so or not." -- Illustrated Commentary upon the Bible.

2 - Dr Geddes translates the clause, "Their hearts have they hardened." "Literally," says he, "they have closed their midriff; -- shut out all compassion from their hearts." The Hebrew word which is rendered fat is explained by Gesenius, when used figuratively, as denoting a fat, that is, an unfeeling heart.

They are enclosed in their own fat - The meaning here is, that they were prosperous, and that they were consequently self-confident and proud, and were regardless of others. The phrase occurs several times as descriptive of the wicked in a state of prosperity, and as, therefore, insensible to the rights, the wants, and the sufferings of others. Compare Deuteronomy 32:15, "But Jeshurun waxed fat and kicked: thou art waxed fat, thou art grown thick, thou art covered with fatness; then he forsook God which made him," etc. Job 15:27, "because he covereth his face with his fatness, and maketh collops of fat on his flanks." Psalm 73:7, "their eyes stand out with fatness." Psalm 119:70, "their heart is as fat as grease."
With their mouth they speak proudly - Haughtily; in an arrogant tone; as a consequence of their prosperity.

They are enclosed in their own fat - Dr. Kennicott, Bishop Horsley, Houbigant, and others, read the passage thus: עלי חבלמו סגרו alai chablamo sageru, "They have closed their net upon me." This continues the metaphor which was introduced in the preceding verse, and which is continued in the two following: and requires only that עלי ali, "upon me," should began this verse instead of end the preceding; and that חלב cheleb, which signifies fat, should be read חבל chebel, which signifies rope, cable, or net. This important reading requires only the interchange of two letters. The Syriac translates it, shut their mouth: but the above emendation is most likely to be true.
They speak proudly - Having compassed the mountain on which I had taken refuge, they now exult, being assured that they will soon be in possession of their prey.

They are inclosed in their own (i) fat: with their mouth they speak proudly.
(i) They are puffed up with pride, as the stomach that is choked with fat.

They are enclosed in their own fat,.... Or "their fat has enclosed them"; either their eyes, that they can hardly see out of them, or their hearts, so that they are stupid and senseless, and devoid of the fear of God; the phrase is expressive of the multitude of their wealth and increase of power, by which they were swelled with pride and vanity, and neither feared God nor regarded man; so the Targum paraphrases it,
"their riches are multiplied, their fat covers them;''
see Deuteronomy 32:15; some read it, "their fat shuts their mouths", so Aben Ezra and Kimchi; or "with their fat they shut them" (h); but the accent "athnach" will not admit of this reading; the last word belongs to the next clause;
with their mouth they speak proudly; against God and his people, belching out blasphemies against the one, and severe menaces and threatenings against the other.
(h) So De Dieu.

enclosed . . . fat--are become proud in prosperity, and insolent to God (Deuteronomy 32:15; Psalm 73:7).

Psalm 17:10 tell what sort of people these persecutors are. Their heart is called fat, adeps, not as though חלב could in itself be equivalent to לב, more especially as both words are radically distinct (חלב from the root לב, λιπ; לב from the root לב, לף to envelope: that which is enveloped, the kernel, the inside), but (without any need for von Ortenberg's conjecture חלב לבּמו סגרוּ "they close their heart with fat") because it is, as it were, entirely fat (Psalm 119:70, cf. Psalm 73:7), and because it is inaccessible to any feeling of compassion, and in general incapable of the nobler emotions. To shut up the fat = the heart (cf. κλείειν τὰ σπλάγχνα 1-John 3:17), is equivalent to: to fortify one's self wilfully in indifference to sympathy, tender feeling, and all noble feelings (cf. השׁמין לב = to harden, Isaiah 6:10). The construction of פּימו (which agrees in sound with פּימה, Job 15:27) is just the same as that of קולי, Psalm 3:5. On the other hand, אשּׁוּרנוּ (after the form עמּוּד and written plene) is neither such an accusative of the means or instrument, nor the second accusative, beside the accusative of the object, of that by which the object is surrounded, that is usually found with verbs of surrounding (e.g., Ps 5:13; Psalm 32:7); for "they have surrounded me (us) with our step" is unintelligible. But אשׁורנו can be the accusative of the member, as in Psalm 3:8, cf. Psalm 22:17, Genesis 3:15, for "it is true the step is not a member" (Hitz.), but since "step" and "foot" are interchangeable notions, Psalm 73:2, the σχῆμα καθ ̓ ὅλον καὶ μέρος is applicable to the former, and as, e.g., Homer says, Iliad vii. 355: σὲ μάλιστα πόνος φρένας ἀμφιβέβηκεν, the Hebrew poet can also say: they have encompassed us (and in fact) our steps, each of our steps (so that we cannot go forwards or backwards with our feet). The Ker סבבוּנוּ gets rid of the change in number which we have with the Chethb סבבוני; the latter, however, is admissible according to parallels like Psalm 62:5, and corresponds to David's position, who is hunted by Saul and at the present time driven into a strait at the head of a small company of faithful followers. Their eyes - he goes on to say in Psalm 17:11 - have they set to fell, viz., us, who are encompassed, to the earth, i.e., so that we shall be cast to the ground. נטה is transitive, as in Psalm 18:10; Psalm 62:4, in the transitively applied sense of Psalm 73:2 (cf. Psalm 37:31): to incline to fall (whereas in Psalm 44:19, Job 31:7, it means to turn away from); and בּארץ (without any need fore the conjecture בּארח) expresses the final issue, instead of לארץ, Psalm 7:6. By the expression דּמינו one is prominently singled out from the host of the enemy, viz., its chief, the words being: his likeness is as a lion, according to the peculiarity of the poetical style, of changing verbal into substantival clauses, instead of דּמה כּאריה. Since in Old Testament Hebrew, as also in Syriac and Arabic, כ is only a preposition, not a connective conjunction, it cannot be rendered: as a lion longs to prey, but: as a lion that is greedy or hungry (cf. Arab. ksf, used of sinking away, decline, obscuring or eclipsing, growing pale, and Arab. chsf, more especially of enfeebling, hunger, distinct from חשׂף = Arab. ks̆f, to peel off, make bare) to ravin. In the parallel member of the verse the participle alternates with the attributive clause. כּפיר is (according to Meier) the young lion as being covered with thicker hair.

They - They live in splendor and prosperity.