The Temple in Jerusalem was known as "the house of God" (2 Cor. 5:14) and "the house of YHVH" (1 Kings 8:10). However, we may conclude that this is not the "Father's house" to which Yeshu'a was referring, since that very house would be destroyed in 70 A.D. The physical Temple in Jerusalem had no further relevance to the body of Christ after Christ offered the ultimate sin offering (Heb. 10:10).
The KJV translates the Greek word μονή (monē) here as "mansions," but in v. 23 of the same chapter, it translates it as "abode." The English translation of "mansions" comes from the Vulgate which has mansiones. The Latin word mansio, like the Greek word μονή, simply means "dwelling" or "abobe." It did not have the same sense that the English word "mansion" possesses today, i.e. a grand estate.
The Greek verb ἑτοιμάζω (hetoimazō), meaning "to prepare," also occurs in another Johannine text, Rev. 21:2, in which it is written,
And I, Yochanan, saw the holy city, new Jerusalem, coming down from God out of heaven, prepared (ἡτοιμασμένην) as a bride adorned for her husband.
Many believe that the place to which Yeshu'a refers is "heaven," but may I say, I do not believe heaven needs preparation, for it is the holy abode of God Himself created in the beginning.
On the other hand, the holy city, new Jerusalem, comes out of heaven and is indeed said to be prepared (cp. Rev. 21:2). I would also propose that the holy city of new Jerusalem is the body of Christ itself, i.e. the Church.
For, just as new Jerusalem is said to be "prepared as a bride adorned for her husband," elsewhere, the apostle Paulos writes (2 Cor. 11:2), "I have espoused you to one husband, so that I may present [you as] a chaste virgin to Christ." Furthermore, he writes that (Eph. 5:25-27) "Christ also loved the church, and gave himself for it...so that he may present it to himself a glorious church, not having spot, or wrinkle, or any such thing, but that it should be holy and without blemish."
As both new Jerusalem and the Church are said to be the bride of Christ, I can only reason that new Jerusalem is indeed the Church, lest Christ be an adulterer.
If this is so, then the place that Yeshu'a is preparing is not only new Jerusalem, but the Church itself.
But, let each study the scripture and show himself approved.