The lover/speaker has lost his beloved but intends to make the most of this one last ride together. He then goes forward with a series of justifications to show how his love and this one last ride are worthwhile. In the fifth stanza, the speaker notes that his experience riding with his beloved is better than the statesman's legacy which is merely ten lines upon a gravestone or history book. His last ride is also better than the soldier's legacy which amounts to a short life with a significant but brief monument/grave. In the next stanza, the speaker admits the poet's art is significant ("'Tis something; nay, tis' much"). However, he prefers his actual experience to the poet's rhymes. In the next stanza, the speaker adds that the sculptor makes himself a slave to his art while he (speaker) is at least a slave to a real, living "Venus" who "fords" (rides) over the "burn" (creek): 

And you, great sculptor--so, you gave

A score of years to Art, her slave,

And that's your Venus, whence we turn

To yonder girl that fords the burn! 

Again, the speaker notes that his riding experience is better than the musician's notes because music goes out of fashion. In the end, the speaker considers how heavenly it would be if this ride would last forever. In each case, the speaker seeks to justify (to the reader and to himself) that this one last ride holds as great, if not greater, significance as other passionate pursuits.