Owen uses a simile to describe the soldiers. We know this in the quote “like old beggars”. The word “beggars” suggests that the soldiers’ clothes are very scruffy and covered in mud. They probably haven’t washed either so they will be smelly and look very scruffy.
Like a man in fire
Dulce et decorum est pro patria mori! :-D
The Dad is telling the son that it is a good thing to go to war and die for your country. However, the author thinks this is a Bie Lie!