In just a few lines, the speaker admits something a little embarrassing: sitting feels good, and getting up does not. "My seat / pleases me" sounds contented, almost smug. But the next phrase, "but not / to stand and walk," pulls the other way. The pleasure of sitting is tied to a reluctance to move, so the comfort comes with a faint note of guilt or inertia.
The last two lines turn this into something bigger. "A hard matter / is pleasure" can be read a few ways. Maybe pleasure is hard to resist, or hard to give up once we have it. Maybe real pleasure is difficult to find or understand. The sentence order feels slightly twisted, as if the speaker is still working it out.
The mood is quiet, wry, and a bit lazy. The short, broken lines mimic someone settling in and pausing to think, and the title, "Sedentary," names the habit with a gentle shrug.