Implicit Costs - Implied Rental Rate

Hi all, I am new to this forum, and was hoping if someone can resolve my uncertainty in one of the topic in the Economic section According to the Schweser book 2, Implied Rental Rate is as following Sum of (1) economic depreciation, which is the decrease inthe value of a firm’s assets over time, and (2) foregone interest. I understand the second point, foregone interest, but am a bit confused at the first part. Are we including economic depreciation because the depreciated value can be invested somewhere else? According to the book, implied rental rate is what the firm could have earned if it had rented its capital to another firm. Not sure how depreciation can fit into that definition. Thanks in advance for your help.