Surely translates a conjunction that gives emphasis to what follows; it can be rendered “I am certain (or, sure) that.” Or else the word can mean “Only,” so that the translation can be “Nothing but your goodness and love.”
Mercy translates the word which in 5.7 is translated “steadfast love.” Yahweh’s “goodness and love” are pictured as his messengers, which accompany the psalmist (see similar language in 43.3; 85.10–11).
Good News Translation has recast goodness and mercy into “your goodness and love.” In some languages it is not possible to speak of abstract qualities as following or accompanying someone. It is more often natural for someone to do or be characterized by these qualities. Therefore it is sometimes necessary to say, for example, “because you are good and because you love me, you will be with me all my life.”
The verb translated follow means “to accompany,” “to go with”; it should not be given the meaning of “to pursue, to run after.”
I shall dwell: the verb appears in the Masoretic text as a form which means “I shall return” (so Bible en français courant); but the Hebrew consonants can be read with other vowels (following the Septuagint) to mean I shall dwell, which is done by most commentators and translations. Hebrew Old Testament Text Project says that all ancient versions and ancient Jewish grammarians took the verb to mean “to sit down, to dwell.” There are two possible interpretations: (1) “and I shall dwell” or (2) “and I shall return.”
The house of the LORD is most probably a reference to the Temple. The meaning of the psalmist’s declaration is that he wants to worship Yahweh in the Temple all his life or, in an extended sense, always to experience Yahweh’s presence and power with him. Anchor Bible, however, takes the house of the LORD to be Yahweh’s heavenly abode, in which the psalmist wants to live forever. The expression the house of the LORD may be the local designation of a church building. If that is the case, it will be better to speak of the Temple in Jerusalem.
For ever: the Hebrew phrase “length of days” at the end of the verse is taken by most to mean “a very long time,” “as long as I live” (Good News Translation, Bible en français courant, Die Bibel im heutigen Deutsch; see 21.4; 91.16). New Jerusalem Bible has “for many long years,” New Jerusalem Bible “for all time to come,” and Biblia Dios Habla Hoy “and in your house, O Lord, I will live always.”
Quoted with permission from Bratcher, Robert G. and Reyburn, William D. A Handbook on the Book of Psalms. (UBS Helps for Translators). New York: UBS, 1991. For this and other handbooks for translators see here .