So what is God talking about when the New Testament speaks of us getting a mansion? Let's think about that for a moment. Is that what heaven is really all about? Living out our days in the hopes that we are going to get a huge house to live in? Let's not trivialize the heart and purpose of the Bible in such a way! The Apostle Paul did not say that there was "one thing" that he pressed on for - to get a big mansion! What did he say? My "ONE THING" is to KNOW CHRIST!
The passage on "mansions" is found in John 14. The key to understanding John 14 is to read it in light of John 13. CONTEXT!!!
In John 13, Jesus has told them that He is going to go away, and they cannot go with Him. They are saddened at this news, of course. But then He tells them to not be troubled because He is going to prepare a place for them, in the Father's house are many "mansions". In doing do, He says that He will return for them again, and receive them unto Himself, that where He is they will be. Also, the heart behind this passage is intimate relationship, not a construction project.
What troubled them is separation. Once you have tasted God, you want all of God, and cannot stand the thought of separation from God. Now focus on the word "mansions".... the word is really dwelling places or as I would translate it "abidings". Jesus is going to prepare places for "abiding" - places where He and us can live together in union. And note that He says as soon as He prepares that place, He will return and we will be received unto Him.
May I suggest, that this has nothing to do with mansions in the sky that we have to wait for heaven to be able to have Jesus receive us! In the context, the place He went to prepare is us! Rom 6 tells us that He took us to the cross. There, He killed our old man, our old sinful self and resurrected us brand new creations (II Cor 5:17). Having now been "prepared", having been made right, He the RIGHT ONE could now come back to us and live in us, through the presence of the Holy Spirit. Now He could receive us unto Himself so that we could be with Him (seated in Heaven right now Eph. 2:6) and so that He could be with us wherever we go.
This is our true "ONE THING" --- to know Christ! The greek word for "know" there is ginosko = which means to know by experience. I do not believe that God made a bunch of big houses for us to dwell in in heaven, but I do believe He "prepared us" as the place of His own residence so that we could be with Him and experience Him forever.... starting right now and continuing in union with Him when we leave this earth. WOW!