Does it Matter? - Siegfried Sassoon

Does it matter?—losing your legs?...

Repetition involving the thought of 'does it matter?' emphasises the pondering he does as to whether any of the losses he has dealt with truly means anything.

For people will always be kind,

He is wondering if it means anything to have experienced a loss right in front of your own eyes - possibly haunting you for eternity when you're both awake and asleep - when you will have the kindness, respect, and admiration from your peers until the day you die and possibly afterwards too.

And you need not show that you mind

When the others come in after hunting

To gobble their muffins and eggs.

Does it matter?—losing your sight?...

There’s such splendid work for the blind;

And people will always be kind,

This repeated line almost verbatim to the one above stresses the bittersweet glory he gets for fighting and surviving long enough to process the propaganda that had most definitely been the main contributor to his eagerness to unknowingly pursue a harrowing ordeal.

As you sit on the terrace remembering

And turning your face to the light.

Do they matter?—those dreams from the pit?...

Noticeable shift in the question, it is now referencing a recurring event, 'dreams' is in a plural form, there is no word of it ending or having ended meaning that the memories have stayed with him in his mind where he can't control the frequency, the timing, etc. He is a slave to his own mind replaying his darkest days even when he came home 'in one piece' long ago.

You can drink and forget and be glad,

He now has the privilege to drinks and celebrations; the end of both his country and his own war, he has all the opportunities in the world to be praised, glorified, and made to be a hero, rightfully so. He now has the privilege to be joyful.

And people won’t say that you’re mad;

And the people who do see the side effects of the horrors will at most look on in pity, understanding in a way which is both ignorant and oblivious.

For they’ll know you’ve fought for your country

For he has done the greatest of services! He has fought and won, he has proven his worth to his country for grappling the heavy weight of death and destruction.

And no one will worry a bit.