The interpretation timeline
Psalm 99:5 Douay-Rheims

For the Lord is sweet, his mercy endureth for ever, and his truth to generation and generation.

A.D. 430 – 1849 4 witnesses

Patristic

before A.D. 750
430
A.D.
Augustine of Hippo Patristic
A.D. 354–430
“"His mercy is everlasting." For He will not cease to be merciful, after He has freed you: it belongs to His mercy to protect you even unto eternal life. "His mercy," therefore, "is to everlasting: and His Truth from generation to generation" [Psalm 100:5]. Understand by "from generation to generation," either every generation, or in two generations, the one earthly, the other heavenly. Here there is one generation which produces mortals; another which makes such as are everlasting. His Truth is both here, and there. Imagine not that His truth is not here, if His truth were not here, he would not say in another Psalm: "Truth is risen out of the earth;" nor would Truth Itself say, Lo, I am with you always, even unto the end of the world. [Matthew 28:20]”
Source

Scholastic

c. 1100 – 1500
1105
A.D.
Rashi Jewish
1040–1105
“and until generation after generation His faith will endure. Every expression of truth (אמת) and faith (אמונה) means the realization of a promise, that He makes true and assures His promise.”

Post-Reformation

c. 1650 – 1900
1771
A.D.
John Gill Reformed
1697–1771
“For the Lord is good,.... Both in a providential way, and in a way of grace, and does good; he is the good Shepherd, that has laid down his life for the sheep; and the good Samaritan, that pours in the wine and oil of his love and grace, and his precious blood, to the healing of the wounds made by sin: while he was on earth, he went about doing good to the bodies and souls of men; and he continues to do good unto them, and therefore should be praised, served, and worshipped: his mercy is everlasting; or "his grace" (e); there is always a sufficiency of it for his people; and his lovingkindness, which may be also here meant, is always the same; having loved his own which were in the world, he loves them to the end, Joh 13:1. and his truth endureth to all generations; or his faithfulness in fulfilling his promises, and performing his engagements; he was faithful to his Father that appointed him, and to the covenant he made with him; and he is faithful to his people, to keep what they commit to his care and charge now, and to give them the crown of righteousness at the last day, which is laid up for them; and upon all these considerations, and for these reasons, ought to be praised and adored. (e) "gratia ejus", Cocceius, Gejerus; "gratia et misericordia ejus", Michaelis. Next: Psalms Chapter 101”
Source
1849
A.D.
1774–1849
“Truth. This is commonly joined with mercy. (Calmet) — God faithfully executes what he has promised (Worthington) for the liberation of his people, and the conversion of the Gentiles. (Calmet) Bible Text & Cross-references: All are invited to rejoice in God, the Creator of all. 1 A psalm of praise. 2 Sing joyfully to God, all the earth: serve ye the Lord with gladness. Come in before his presence with exceedingly great joy. 3 Know ye that the Lord, he is God: he made us, and not we ourselves. We are his people and the sheep of his pasture. 4 Go ye into his gates with praise, into his courts with hymns: and give glory to him. Praise ye his name: 5 for the Lord is sweet, his mercy endureth for ever, and his truth to generation and generation. Table of Psalms 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 Lorem ipsum dolor sit amet, consectetur adipiscing elit. Quisque finibus commodo nibh, ut elementum velit sollicitudin at. Donec suscipit commodo risus. Nunc vel orci eget ligula elementum consequat. Fusce velit erat, convallis scelerisque aliquet ut, facilisis egestas tellus. Quisque sit amet sapien placerat, ultricies sapien ut, vestibulum ex.”
Source
Modern · 1953 →

The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.