The honoring of ancestors is something that occurs in cultures around the world; the honoring of and praying for the Dead is a venerable Christian tradition as well.
There are questions that come up concerning the honoring of ancestors, of course; how does this fit in with reincarnation? If we're reborn, how do we honor the Dead? Why would we honor people that are, in fact, already living in the world again?
This is a valid question, one that I asked for many years, but it's based on an incomplete perspective of what rebirth means, especially when we bring in Buddhist cosmology. Rebirth doesn't mean that one is reborn into this world immediately, and many people are probably reborn into Heavenly Realms. Moreover, the lifespans in those Heavenly Realms, while not eternal, are longer than our lives on Earth- at least according to the Buddhist traditions.
So, in that sense, at least some of our ancestors really are both 1) going to one day be reborn AND 1) are worthy of our regard and veneration (if they're of the Heavenly Realms).
Even then (and this important), we're not privy to how long it takes for one to be reborn after passing away from this world. The transition period between life cycles may be longer than several of our human life cycles.
The ultimate point is this: when taken as a group, some of your ancestors are 100% in the Realms of the Afterlife, and they can be affected by us and vice-versa. And it's important to recognize that.
Tomorrow we'll continue with another post about the Ancestors.