You are asking about this passage from John 14:2-3: "In my Father's house there are many dwelling places. If it were not so, would I have told you that I go to prepare a place for you? And if I go and prepare a place for you, I will come again and will take you to myself, so that where I am, there you may be also" (NRSV).
As you noted, this passage – originally intended to forewarn his disciples in advance of Jesus' imminent arrest and death – has long been used to comfort those who are grieving a death. It's a remarkable affirmation that death is not the ending of anything. It is, as James Dillet Freeman describes it, "the opening and closing of a door." We simply move on to other places in the infinite realm of Spirit. And the more we become aware of these infinite possibilities, the more freely we can move from one “place” – one dimension, perhaps – to another.
I would agree that the same understanding serves us well as we work within this particular “place” – this mortal experience. Even – perhaps especially – as we grow in spiritual understanding, we often feel limited and confined within these human bodies. We tend to assume that any expansion into other realms will have to wait until we put the bodies down. But the Truth is that we are not – cannot be – limited in any way. We can easily explore other "places" – other dimensions of the infinite realm of Spirit – through meditation, imagination, dreams and a myriad of other exercises of our divine powers. The more conscious we are, the freer we are. And we don't have to wait until we die to expand into more and more of our true spiritual energy.