What is meaning of "My Father's House"?
Many Rooms
The Greek word used translated here "rooms" and "home" is the same word #3438 monai. This word only occurs 2x's and is more properly translated "dwelling place although it has sometimes been translated "mansions". The translation using mansion has led to misunderstanding and focusing entirely on the wrong thing. Our English copies ended up using the word “mansions” because the Vulgate (the Latin version of the Bible used until the time of the Reformation) used the word “mansiones” in verse 2. But this does not carry the same connotation as our modern understanding of “mansion.” The meaning of the Latin, “mansiones,” is “living-places.”
So the more applicable translation is "dwelling place".
Meaning of Verse 2: speaks about the day when we will dwell with the Godhead in eternity
Meaning of Verse 23: Jesus explains that even here and now all the members of the Godhead dwell with believers. Until we can dwell directly in their presence, the Father and the Son, in the Holy Spirit (see chapters 14-16), will come and dwell with us...in the hearts of believers.
Preparing a Place for You
An understanding of the meaning of My Father's House and the many rooms that is groundwork for understanding what Jesus means when He says, “I go to prepare a place for you.” But also understanding the greater context o chapter's 13 and 14 is also very significant.
Chapter 13 opens with "It was just before the Passover Festival. Jesus knew that the hour had come for him to leave this world and go to the Father. Having loved his own who were in the world, he loved them to the end."
Jesus has already told the disciples that He is going away so that they are troubled in heart. This is precisely the reason for His words in John 14:1, “Let not your hearts be troubled neither let them be afraid.”
It is only as we read the words of John 14:1,2 in light of Hebrews 9-10 (which speak of the heavenly Temple being sanctified with the blood of Christ) that we come to understand that our Lord is speaking about going to the cross to prepare a place for His own. Jesus Christ came into the world to “go” to the cross. He would return to the Father by means of His atoning death and resurrection.
A.W. Pink made the following observations:
He does not (at this time) explain how the place in the Father’s house should be prepared for them; nor were they yet, perhaps, able to understand. The Epistle to Hebrews will show us, if we turn to it, that the heavenly places had to be purified with the better sacrifices which He was to offer, in which all the sacrifices of the law would find their fulfillment. Ephesians speaks similarly of the ‘redemption of the purchased possession;’ and Colossians of the ‘reconciliation of things in heaven’ (Heb. 9:23; Eph. 1:14; Col. 1:20).
“I go to prepare a place for you.” We understand this to mean that the Lord Jesus has procured the right–by His death on the cross–for every believing sinner to enter heaven. He has prepared for us a place there by entering Heaven as our representative and taking possession of it on behalf of His people. He has prepared for us a place by entering the ‘holy of holies‘ on High as our great High Priest carrying our names in with Him. Christ would do all that was necessary to secure for His people a welcome and permanent place in Heaven.
So we see that it was by the blood that He shed on the cross that Jesus prepared a place for us in the Father’s house. We are made kings and priests to our God and are given a place to dwell with Him in the Heavenly Temple. It is now our reward to be with the One who secured this for us by His death and resurrection. This is why Jesus finally brings comfort to the disciples in John 14:3 by saying, “If I go to prepare a place for you, I will come again and receive you to Myself that where I am there you may be also.” Come Lord Jesus, bring us to our eternal dwelling place.
Reference: http://feedingonchrist.com/how-does-christ-prepare-a-place-for-us/