[…] There shall be In that rich earth a richer dust concealed (3-4)
The word "rich" suggests that the natural world—land—has a value. It is worth so much, sometimes, that people will kill for it. It is, however, not worth as much as human life, which is "richer."
A dust whom England bore, shaped, made aware (5)
The natural world is given a big role here. "England" is a country, but it is also land—rivers, mountains, hills, etc. The natural world gave birth to the soldier, "shaped" him, "made" him "aware." Keep an eye on that. The natural world's role will be stressed again later.
A body of England's, breathing English air, Washed by the rivers, blest by suns of home (7-8)
The passive construction here is interesting. The rivers and the suns do all the work, all the washing and blessing. This points to the active role that one's natural surroundings play in one's development as a human being.
Her sights and sounds; dreams happy as her day; And laughter, learnt of friends; and gentleness, In hearts at peace, under an English heaven (12-14)
In death, the speaker is reunited with the natural world that "bore" and "shaped" him. In the "English heaven," he re-experiences England's "sights and sounds," which must in part refer to her natural features (rivers, hills, animals, and the like).