In the very first couplet, Kipling addresses the "God of our fathers," immediately putting the British Empire on talking terms with God. The reason for addressing the "Lord God of Hosts" becomes clear as the stanza moves on. Allusion to familiarity with the Almighty enhances the impression about the power and prestige of the Empire.
The "awful hand" of God phrase recognizes the respect and honor that needs to be given to the God who has allowed the British Empire to spread over such a wide and varied domain; "dominion over palm and pine." Aside from the alliteration, the contrasting trees reinforce the variation in climate and plant life encompassed within the Empire.
Kipling mentions that the relationship with God has been in place for a long time ("known of old") and refers to the vast area included in the British Empire with another alliteration - the "far-flung battle line."