With this term "Heaven" we wish to say that God, the God who made himself close to us, does not abandon us in or after death but keeps a place for us and gives us eternity. We mean that in God there is room for us.
To understand this reality a little better let us look at our own lives. We all experience that when people die they continue to exist, in a certain way, in the memory and heart of those who knew and loved them.
We might say that a part of the person lives on in them but it resembles a "shadow" because this survival in the heart of their loved ones is destined to end.
God, on the contrary, never passes away and we all exist by virtue of his love. We exist because he loves us, because he conceived of us and called us to life. We exist in God's thoughts and in God's love. We exist in the whole of our reality, not only in our "shadow".
Our serenity, our hope and our peace are based precisely on this: in God, in his thoughts and in his love, it is not merely a "shadow" of ourselves that survives but rather we are preserved and ushered into eternity with the whole of our being in him, in his creator love.
It is his Love that triumphs over death and gives us eternity and it is this love that we call "Heaven": God is so great that he also makes room for us. And Jesus the man, who at the same time is God, is the guarantee for us that the being-man and the being-God can exist and live, the one within the other, for eternity.