then middle-earth mankind's Guardian, eternal Lord, afterwards made (7-8)
It's interesting to see the intersection of eternal with earthly time here. On the one hand, we have the relative, earthly time markers "then" and "afterwards," which date the historical creation of the earth. But in the middle we also have "eternal," an adjective applied to God, that reminds us that this dude has lived forever—no "first," "then," or "afterwards" for him.
eternal Lord (4, 7)
Since this title is the only one used twice, it must be important. Maybe "eternal" is the most important adjective to attach to God, since, if he doesn't last forever, all his other attributes—his holiness and might—will also disappear.