The psalm begins with a universal call: praise the Lord, all nations, extol him, all peoples. It is surprising in a psalm that is part of Israel's worship: Gentiles, and not only Israelites, are invited to praise. The poet does not limit worship to the covenant people but extends it to all humanity.
Verse 2 gives the reason for that universal praise. The Lord's steadfast love is great toward us, and the faithfulness of the Lord endures forever. Here us refers to Israel, which has received God's mercy, and God's faithfulness toward them is a reason for the nations to praise him. The two words, steadfast love and faithfulness, sum up the character of the Lord in the Old Testament: his loyal love and his fidelity.
The psalm ends with hallelujah, praise the Lord, the same word with which many psalms begin and end.