Ps 50:18

“See who this is: David as one man was seeming to implore; see ye here our image and the type of the Church. "Deal kindly, O Lord, in Your good will with Sion" [Psalm 51:18]. With this Sion deal kindly. What is Sion? A city holy. What is a city holy? That which cannot be hidden, being upon a mountain established. Sion in prospect, because it has prospect of something which it hopes for. For Sion is interpreted "prospect," and Jerusalem, "vision of peace." You perceive then yourselves to be in Sion and in Jerusalem, if being sure ye look for hope that is to be, and if you have peace with God. "And be the walls of Jerusalem built." "Deal kindly, O Lord, in Your good will with Sion, and be the walls of Jerusalem built." For not to herself let Sion ascribe her merits: do Thou with her deal kindly, "Be the walls of Jerusalem built:" be the battlements of our immortality laid, in faith and hope and charity.”

“Sacrifice. If my crime were of such a nature as to be expiated by certain victims, I would surely have offered them: but my heart has offended, and must do penance. (Calmet) — The legal victims were not of themselves sufficient to remit sin. (Menochius) — Contrition was necessary, Isaias lxvi. 2., and Ezechiel vi. 9. (Berthier) — The Scripture often prefers internal, before outward sacrifices. This of the heart must precede those of justice, and of praise. (Worthington) — The heart must be broken, to make place for love. Compunction is thrice urged. The two first terms in Hebrew are the same, “contrite,” (Haydock) broken, or disconcerted. Kateklasthe philon etor . (Homer, Odyssey) (Menochius) — The captives might adopt this prayer, Daniel iii. 39. (Calmet) — External sacrifices are commended in the next verses, as they are good, (Haydock) being instituted by God. (Menochius)”

“From this spiritual sacrifice, well-pleasing to God, the Psalm now, in vv. 20f., comes back to the material sacrifices that are offered in a right state of mind; and this is to be explained by the consideration that David's prayer for himself here passes over into an intercession on behalf of all Israel: Do good in Thy good pleasure unto Zion. את־ may be a sign of the accusative, for היטיב (הטיב) does take the accusative of the person (Job 24:21); but also a preposition, for as it is construed with ל and עם, so also with את in the same signification (Jer 18:10; Jer 32:41). זבח־צדק are here, as in Psa 4:6; Deu 33:19, those sacrifices which not merely as regards their outward character, but also in respect of the inward character of him who causes them to be offered on his behalf, are exactly such as God the Lawgiver will have them to be. By כּליל beside עולה might be understood the priestly vegetable whole-offering, Lev 6:15. (מנחת חבתּין, Epistle to the Hebrews, ii. 8), since every עולה as such is also כּליל; but Psalm-poetry does not make any such special reference to the sacrificial tra. וכליל is, like כליל in Sa1 7:9, an explicative addition, and the combination is like ימינך וזרועך, Psa 44:4, ארץ ותבל, Psa 90:2, and the like. A שׁלם כּליל (Hitzig, after the Phoenician sacrificial tables) is unknown to the Israelitish sacrificial worship. The prayer: Build Thou the walls of Jerusalem, is not inadmissible in the mouth of David; since בּנה signifies not merely to build up what has been thrown down, but also to go on and finish building what is in the act of being built (Psa 89:3); and, moreover, the wall built round about Jerusalem by Solomon (Kg1 3:1) can be regarded as a fulfilment of David's prayer. Nevertheless what even Theodoret has felt cannot be denied: τοῖς ἐν Βαβυλῶνι...ἁρμόττει τὰ ῥήματα. Through penitence the way of the exiles led back to Jerusalem. The supposition is very natural that vv. 20f. may be a liturgical addition made by the church of the Exile. And if the origin of Isa 40:1 in the time of the Exile were as indisputable as the reasons against such a position are forcible, then it would give support not merely to the derivation of vv. 20f. (cf. Isa 60:5, Isa 60:7, Isa 60:10), but of the whole Psalm, from the time of the Exile; for the general impress of the Psalm is, according to the accurate observation of Hitzig, thoroughly deutero-Isaianic. But the writer of Isa 40:1 shows signs in other respects also of the most families acquaintance with the earlier literature of the Shı̂r and the Mashal; and that he is none other than Isaiah reveals itself in connection with this Psalm by the echoes of this very Psalm, which are to be found not only in the second but also in the first part of the Isaianic collection of prophecy (cf. on Psa 51:9, Psa 51:18). We are therefore driven to the inference, that Ps 51 was a favourite Psalm of Isaiah's, and that, since the Isaianic echoes of it extend equally from the first verse to the last, it existed in the same complete form even in his day as in ours; and that consequently the close, just like the whole Psalm, so beautifully and touchingly expressed, is not the mere addition of a later age.”