The third (and fourth) verse of Psalm 115 feature in the Ordinary of the Mass (Vetus Ordo) as the prayer the priest says before he receives the Precious Blood, and thus completes the sacrifice of the Mass:
Quid retríbuam Dómino, * pro ómnibus, quæ retríbuit mihi?
What shall I render to the Lord, for all the things that he has rendered to me?
Quid (what) retríbuam (I shall repay/render/give back) Dómino (to the Lord)
retribuo, tribui, tributum, ere 3, to repay, requite, reward, recompense, render; give back, return; make requital for
This verse poses an important question: what can we possibly offer God?
God, after all, made all things, including us. And, as the previous verse points out, in the main we have repaid him with lies and deceit. As St Augustine comments:
"What had preceded, on the man's part, save sins? ...for such was the return of those who said, This is the heir: come, let us kill him (Matthew 21:38)."
Yet what has God rendered to us? Cassiodorus instructs that it is the hope of the Resurrection, and promise of the kingdom of heaven. God, in short, repays good for our evil.
All the same, the question models for us an attitude of thankfulness that we ought to cultivate, as Chrysostom comments:
"...this is the mark of a thankful attitude, busying oneself and searching how to repay something to the benefactor for what had been received, and after paying everything to think one has given nothing worthwhile."
Christina Rossetti's poem, In the Bleak Midwinter provides a wonderful meditation on this verse. Here it is:
In the bleak mid-winter Frosty wind made moan,
Earth stood hard as iron, Water like a stone;
Snow had fallen, snow on snow,Snow on snow,
In the bleak mid-winter / Long ago.
Our God, Heaven cannot hold Him Nor earth sustain;
Heaven and earth shall flee away When He comes to reign:
In the bleak mid-winter A stable-place sufficed The Lord God Almighty, Jesus Christ.
Enough for Him, whom cherubim Worship night and day,
A breastful of milk And a mangerful of hay; Enough for Him, whom angels Fall down before,
The ox and ass and camel Which adore.
Angels and archangels May have gathered there, Cherubim and seraphim Thronged the air,
But only His mother In her maiden bliss, Worshipped the Beloved With a kiss.
What can I give Him, Poor as I am?
If I were a shepherd I would bring a lamb,
If I were a wise man I would do my part,
Yet what I can I give Him, Give my heart.
The Catechism of the Catholic Church (222-4) teaches:
Believing in God, the only One, and loving him with all our being has enormous consequences for our whole life. It means coming to know God's greatness and majesty: "Behold, God is great, and we know him not." Therefore, we must "serve God first". It means living in thanksgiving: if God is the only One, everything we are and have comes from him: "What have you that you did not receive?" "What shall I render to the LORD for all his bounty to me?"
1 Crédidi, propter quod locútus sum: * ego autem humiliátus sum nimis.
2 Ego dixi in excéssu meo: * Omnis homo mendax.
3 Quid retríbuam Dómino, * pro ómnibus, quæ retríbuit mihi?
4 Cálicem salutáris accípiam: * et nomen Dómini invocábo.
5 Vota mea Dómino reddam coram omni pópulo ejus: * pretiósa in conspéctu Dómini mors sanctórum ejus:
6 O Dómine, quia ego servus tuus: * ego servus tuus, et fílius ancíllæ tuæ.
7 Dirupísti víncula mea: * tibi sacrificábo hóstiam laudis, et nomen Dómini invocábo.
8 Vota mea Dómino reddam in conspéctu omnis pópuli ejus: * in átriis domus Dómini, in médio tui, Jerúsalem.
You can find notes on the next verse of the psalm here.