The title sets the scene: the speaker is an advertising man, and the poem reads like his private sales philosophy. He pictures himself in luxurious, almost suffocating images. A bed of oysters suggests indulgence, but also something cold, hard and shell-like, and he says he is "secure as death." That is an odd kind of safety, and it hints that his comfort comes with a chill.
The "severe knight" is harder to pin down. Judging by the imagery, it may stand for a stern, old-fashioned fantasy of strength or honour, and the speaker finds "sure sales" there. The last lines state his cynical conclusion: people want, above all, "the pleasure of loss."
The speaker sounds confident, detached and a little chilling. He treats desire as something he can predict and use. The mood is cool, ironic and unsettling, as if the poem is quietly admitting that advertising works by selling people their own surrender.