Witherington on Going to Heaven and Improving Life on Earth

In my latest reading of Jesus, Paul, and the End of the World, Ben Witherington III says that many modern Christians focus on Christians going to heaven after they die, when the focus of Paul and Jesus was on the resurrection.  Unlike Seventh-Day Adventists, Jehovah's Witnesses, and Armstrongites, however, Witherington does not maintain that Paul believed in soul sleep or denied that the body has a soul that lives on after death, for Witherington contends that I Corinthians 15 is about the clothing of the soul with a new resurrection body.  According to Witherington, Paul treats heaven merely as an intermediate state, whereas he regards the resurrection and God's renewal of creation as much more significant.

I think that many Christians focus on people going to heaven after death because they'd like assurance that their loved ones are alive right now, plus they'd feel more comfortable were their lives to be uninterrupted than they would being in a tomb until the resurrection.  As far as what the "biblical" position is, a body/soul (or spirit) dichotomy does appear to exist in the New Testament (Matthew 10:28; II Corinthians 5).  At the same time, death is called a sleep in the New Testament (I Corinthians 15:51).  Can the two positions be reconciled?  I'm curious as to whether there are other ancient writings that call death a sleep, yet manifest a belief that the dead are conscious in some sort of afterlife.  See also my post here, which talks about how, in the Hebrew Bible, the dead were ordinarily asleep, yet they could be woken up from their rest in Sheol.

Onto another topic, I liked what Witherington said on page 240, in response to the tendency of some to think that Christians should make little effort to improve the world, since Christ will come back and fix everything anyway: "...if one knows that it is God's plan ultimately to renew and redeem the material world, then blessed are they who participate in and foreshadow that by working to clean up the environment, feed the hungry, care for and heal the sick and so bear witness to God's perfect and final will for the world (see Mt 25:31ff.)."