The opening four verses of Psalm 89 contain a trove of theological catch-words from the Old Testament. Verses 1 and 2 are parallel in the proclamation of God's "steadfast love" in their first lines and "faithfulness" in their second. These two traits are central in defining God's character and relationship with Israel. The single Hebrew word translated as "steadfast love" is difficult to convey with any single English expression, and thus we see different English Bibles using a variety of translations in different contexts: steadfast love, loving kindness, love, kindness, mercy, loyalty, favor, devotion, goodness, and still others.
Whatever Ethan the Ezrahite (the psalm's author as stated in the superscription) and his original audience would have heard in these words, for Christians the eternal establishment of the Davidic covenant is accomplished with the coming of Christ. The angel Gabriel's annunciation to Mary expresses this very idea: "the Lord God will give to him the throne of his ancestor David. He will reign over the house of Jacob forever, and of his kingdom there will be no end" (Luke 1:32b-33). Thus when we as Christians read this psalm in worship, we are proclaiming the faithfulness and steadfast love of God as expressed ultimately in Jesus Christ.
Collect for Psalm 89: Mighty God, in fulfillment of the promise made to David’s descendants you established a lasting covenant through your firstborn Son. You anointed your servant Jesus with holy oil and raise him higher than all kings on earth. Remember your covenant, so that we who are signed with the blood of your Son may sing of your mercies forever; through your Son, Jesus Christ our Lord.
 Collect for Psalm 89, For All the Saints A Prayer book for and by the ChurchVol.III © 1995 The American Lutheran Publicity Bureau, Delhi, NY