In All Quiet on the Western Front, Remarque is using Tjaden’s eating as an example to illustrate a statement he made in the previous paragraph. He writes that the soldiers, “in the midst of danger” are “seeking in a wholly unpathetic way a fleeting enjoyment of the hours as they come.” In other words, they are sometimes living in the moment; enjoying life as it comes, when they can.
In the next paragraph, he starts with “It is this, for example, that makes Tjaden spoon down his ham-and-pea soup in such tearing haste when an enemy attack is reported, simply because he cannot be sure that in an hour’s time he will still be alive.”
At this point in the novel, it is almost a surprise that the men can enjoy anything at all—ever. They have been under so much stress and faced so much terror that the reader might expect they could never feel any happiness at all, even at something as simple as a bowl of soup.