God exists = there is life after death?

Many apologists argue that without God there is no purpose to life, no meaning, no higher goals, and existence is meaningless and completely moot.

One question that this should raise but seldom does (even among skeptics) is why exactly would the mere existence of a god give life any "higher" meaning and purpose. What exactly is the connection between "a god exists" and "there is a higher purpose to life"?

What really is happening here is that these apologists are assuming that if there is a god, then there is also life after death (and it matters what we do while we still live, as it affects what happens to us after death.) But why exactly are they making this assumption?

After all, it could be perfectly possible for a god to exist, even one that did create this universe and knows about us and watches us all the time, and there not being any kind of afterlife. It is perfectly possible for there to be a personal god, and death being an absolute end of consciousness. It is perfectly possible for such a god to exist and for our life to be "completely meaningless" (in the sense that these apologists mean it) regardless.

In fact one could actually argue the exact opposite: If there is an afterlife, that makes our earthly lives meaningless, but if there is none, then that makes our earthly lives the most important thing that we have, something that should be cherished and appreciated while we have it.