The letter must explain who is gifting the money, where the donor's funds are coming from and the relationship between the donor and the recipient. A gift letter is an important, formal, legal piece of documentation that can help explain that a (usually rather large) sum of money was gifted to you.A mortgage gift letter is a document that helps satisfy the requirement that a borrower's down payment funds come from legitimate sources. Yes, all lenders will require a gift letter. Although you may have the funds, the lender needs to confirm that you won't have to repay the gift. A gift letter for a mortgage is proof to the lender that money you've been given for your home purchase is a gift, not a loan to be repaid. The most important document required is a gift letter. To use gift funds, you must provide a gift letter proving the money is not a loan. Pennsylvania does not have gift tax however, there is a federal gift tax. A gift letter for a mortgage shows your lender that you don't need to repay gift money toward your down payment.