In John chapter 14 Jesus tells His disciples not to be worried because He has a plan and that plan includes a place (actually a ‘residence’) in heaven prepared for them.
John 14:1-4 Let not your heart be troubled: you believe in God, believe also in Me. 2 In My Father’s house are many mansions: if it were not so, I would have told you. I go to prepare a place for you. 3 And if I go and prepare a place for you, I will come again, and receive you to Myself; that where I am, there you may be also.
Firstly, Jesus identifies Himself as God (verse 1). He speaks with full knowledge as only the omniscient God can. Here He speaks in absolute terms. He does not say “If you stay away from sin, or if you are good, then I will give you a mansion in heaven”. No, His language is definite. The disciples were chosen and from the moment they were saved they had this promise of eternal life in heaven. But they were not saved until later, which we read in John chapter 20. That was after Jesus’ resurrection.
John 20:21,22 Then said Jesus to them again, Peace be to you: as My Father has sent Me, even so send I you. 22 And when He had said this, He breathed on them, and said to them, Receive you the Holy Ghost:
It was then they were born again as real Christians. Jesus breathed His Spirit into them that they might be saved and have the Holy Spirit indwell them. This was a pivotal point in the lives of the disciples as it is in the lives of those saved by God now. All saved Christians have the indwelling Holy Spirit. The Holy Spirit gives the believer an understanding of spiritual things (John 14:26). But at this time, in John 14, they did not have that understanding. Jesus said,
John 14:4,5 And where I go you know, and the way you know. Thomas said to Him, Lord, we know not where You go; and how can we know the way?
Even though Jesus spoke of preparing a place for them in heaven, they did not understand. Jesus even said that they knew where and the way they knew also. But they didn’t have the understanding of the Holy Spirit to recognise it at that time.
John 14:6 Jesus said to him [Thomas], I am the way, the truth, and the life: no man comes to the Father, but by Me.