It is yours with my compliments if you'll just mail the enclosed card. The offer is repeated twice more - once in the fourth paragraph and again in the last paragraph. A letter, unlike an ad or TV commercial, is a personal communication. A formal, stiff, 'corporate' tone is inappropriate for direct mail. You can't fool the reader into thinking direct mail is personal mail.
Personal pronouns help make writing sound like natural conversation.
So do contradictions and an occasional colloquial or slang expression. Here's a sample of appropriate copy style for direct mail. She's so warm, perceptive, and pleasant, you couldn't help but be favorably impressed. Narrow the focus. The most powerful reason for turning to direct mail is that it lets you target your message to select groups of special-interest readers.