Israel has long employed three groups of hymnic praise or "Hallels" in worship:
the "Egyptian Hallel" (Psalms 113-118) recited in the home as a part of Passover celebrations; the "Great Hallel" (Psalms 135-136) recited in the Temple during the slaughter of the lambs at Passover, Tabernacles, and Dedication or Hanukkah; and the "Daily Hallel" (Psalms 145-150) recited every day in the morning synagogue service, even today. In addition, Psalms 146-150--each of which begin and end with Hallelujah "Praise the Lord" form the concluding doxology to the book of Psalms.
Psalm 146 introduces this concluding doxology and thus belongs to the form critical category of Hymn of Praise characterized by an initial summons to praise, bless, thank, or worship the Lord (1b-2) and a reason for that praise (5-9). Of interest here is the way in which that reason comes to light. Instead of the more usual testimony of what God has done for the psalmist, as in Miriam's exuberant cry following their deliverance at the sea (Exodus 15:21b), "Praise the Lord,"(summons to praise) "for he has triumphed gloriously, horse and rider he has thrown into the sea" (reason for praise), the psalmist's witness to God's activity takes the multifaceted form of sapiential instruction (3), illustrative metaphor (4), beatitude (5), then, the expected "reasons" (6-9), and a concluding confession of faith (10a), with "Hallelujahs!" providing an inclusio around the whole (1a,10b).
Another aspect of witness or testimony emerges after a careful consideration of the possessive pronouns attached to "God" throughout the psalm. In verse 2, the psalmist declares his individual intention to praise "my God" throughout his life. The psalmist's individual testimony subtly shifts to the third person in verse 5 where the happiness/blessedness of the "one" (NRSV uses the plural "those/they" for reasons of inclusivity) fortunate enough to have the God of Jacob as "his help" is linked to the one whose hope rests securely in "his God." Finally, verse 10a announces the eternal rule of "your (2ms) God" in Zion.
The formal complexity of the psalm belies its coherent progression of thought and elegant structure:
A Hallelujah! (1a)
B Vow to praise Yahweh "my" God (1b-2)
C Human leaders are powerless and perishable (3-5)
D Creator God (6a)
X Who keeps faith forever (6b)
D' Sustainer God (7a)
C' Yahweh's works are powerful and imperishable (7b-9)
B'Confession of Yahweh "your" God (10a)
A' Hallelujah! (10b)
In this kind of concentric structure we are encouraged to compare the paired sections. Thus, A and A' re identical expressions of praise. B and B' are linked by the words "Yahweh" and "God," as well as the movement from vow to confession. C and C' provide the contrast between powerless and perishable human leaders and the powerful, lasting works of Yahweh that forms the basic message of the psalm. The heart of the psalm proclaims that God, unlike human leaders, "keeps faith forever" (X) a majestic truth framed by the two modes of the divine faith-keeping as "Creator" and "Sustainer" both of which begin with identical participles (oseh) translated "who made" and "who executes" in the NRSV (D, D').
The psalm, then, is framed with "hallelujahs." In between, we are warned against placing our trust in any human being, either the noble ones (nedibim) or the common ones (ben adam) a merism that includes all humanity, and for a very practical reason: human beings eventually die and their thoughts, dreams, plans, and programs die with them. It is better to place our trust in God "who keeps faith forever" (6b). Unlike mere mortals who are powerless, and "in whom there is no salvation" ("help" in NRSV), God is the subject of eleven verbs that portray the divine ability to deliver the goods (6-9). The verbs have been arranged in three groups:
1. In verses 6-7, four participles with an unexpressed subject form the heart of the poem. Here, the proclamation of God's "keeping faith forever" is flanked by descriptions of how this is accomplished: as creator of all that exists and as sustainer who executes justice for the oppressed and gives food to the hungry.
2. In verses 8-9a, five participles introduced by Yahweh as the explicit subject provide a litany of divine compassion as Yahweh releases prisoners, restores sight, lifts up those bowed down, loves the righteous, and protects the stranger.
3. In verse 9b, two imperfect verbs with Yahweh as the implied subject depicts mercy toward the orphan and widow who are upheld and judgment against the wicked.
As to why this psalm was chosen as a response to the First Reading (Ruth 1:1-18), one need only point to this litany of Yahweh's works and wonders in verses 6-9, especially as they are directed toward the support of strangers, orphans, and widows.
The psalm provides a much needed glimpse into God's ultimate care for Naomi and Ruth whose situation looks quite bleak as the book opens with Ruth a non-Israelite stranger pledged to accompany her widowed mother-in-law Naomi. Verses 6-10a also serves to put some meat on Ruth's memorable though skeletal confession of faith in Naomi's God (Ruth 1:16-17).