Move him into the sun -
Him could mean anyone, it is impersonal and helps others relate.
Gently its touch awoke him once,
At home, whispering of fields half-sown.
Fields half-sown, shows lost potential, his life was only half lived and left half sown.
Always it woke him, even in France,
A lot of first world war battles were fought on the French battlefields, refering to this.
Until this morning and this snow.
If anything might rouse him now
Shows the futility of moving him, this is the last resort as if this is the last thing that can be done to try and keep him alive.
The kind old sun will know.
The sun has healing properties, as though it can nurture the soldier back to life, this shows the desperation of the other soliders in their attempt to help their falled comrade.