1 John 3:2 Dear friends, now we are children of God, and what we will be has not yet been made known. But we know that when Christ appears, we shall be like him, for we shall see him as he is.
It is true Christ has not fully explained what we will become other than a new creation, a new being, a pure being who can live with Him in heaven.
But we do know His promises are sure because we have seen them come to pass time and time again. Each time He gives us a promise, we can know we can depend on it fully.
His promises to the people then are written down in History and recorded as coming true. We know, therefore, those further promises written down in our Bibles are true too!