"Buy land, they're not making it anymore." - Mark Twain
One of the many drawbacks of this life is lack. Lack of resources, lack of space, lack of knowledge. It seems the only things this planet has an unlimited supply of are often the things we really don't need, chief among which is sin.
But the Bible paints a different picture of Heaven. It will not be a place where you'll be lucky to rent a flat a full mile away from your place of work. Jesus literally promises us that He is preparing a place specifically for us. Heaven is a glorious Kingdom, and we have our own place there just waiting for us, and it was prepared by none other than the Son of God Himself. This promise is absolute. If it was not the case, Jesus tells us He would not have said it.
It is worth noting that this is in stark contrast to various other gods, particularly Allah. Allah is said to be the best of deceivers (Qur'an 3:54; 8:30). This is to the extent that Abu Bakr, whom Muhammad had personally guaranteed Paradise, said that if he had one foot in Paradise, he would still fear Allah's deceit.
So this "god" is such a trickster that if the seal of his prophets tells you "you're definitely going to Heaven", you could actually set foot in Heaven and still worry that Allah is about to laugh, shout "gotcha", and flick you into eternal Hellfire. But Jesus authoritatively declares "if not, I would have told you."
My brethren, we serve an honest God. There is nothing in His word wherein He is described as a liar, or a trickster, or capricious. From beginning to end, we see a God who never lies, and plans every moment of history. So Holy is this God that even when He wants to go back on His word, all it takes is to remind Him that He gave it (not that He would be capable of forgetting), and He will fulfil it. Just ask Moses, who when the Israelites rebelled, interceded for them in this very manner (Exodus 32:7-14). And here Jesus continues this tradition by telling His disciples that He would have informed them if Heaven had a limited capacity. We have an assurance that we have a great inheritance. We serve a glorious God indeed.