John Lightfoot on Matthew 26:8

[To what purpose is this waste?] It was not without cause that it was called "precious ointment," verse 7, and "very costly," John 12:3: to shew that it was not of those common sorts of ointments used in feasts, which they thought it no waste to pour upon the waiter's head, or to daub upon the wall. But this ointment was of much more value, and thence arose the cavil.