Gustaf Dalman, in his The Words of Jesus (p. 206) writes:
Jesus speaks of a reward ἐν τοῖς οὐρανοῖς, Matt. 5:12 (Luke 623 ἐν τῷ οὐρανῷ), of treasures ἐν οὐρανῷ), Matt. 6:20 (Luke 12:33 ἐν τοῖς οὐρανοῖς), 19:21 (Mark 10:21, Luke 18:22 ἐν οὐρανοῖς). Here “in heaven” stands for “with God”, cf. Matt. 6:1 παρὰ τῷ πατρὶ ὑμῶν τῷ ἐν τοῖς οὐρανοῖς, and Jesus merely means that the recompense of completed work or the compensation for what is sacrificed in this world, is made ready by God even now, in so far as the theocracy (Dalman’s term for the Kingdom of Heaven – MC) is assuredly destined to come for the righteous. Any mystical pre-existence of reward or treasure is in no way contemplated.
“In heaven” means “with God”. It does not mean “existing in another dimension” that is just as much a “place” as this present creation.
N.T. Wright would agree Dalman’s point, I think — or at least, Dalman’s take on “in heaven” meshes with what Wright has said about 1 Peter 1:4:
1 Peter 1.4… speaks of an ‘inheritance which is imperishable, undefiled, unfading, kept in heaven for you, who are being protected by the power of God through faith for a salvation ready to be revealed in the last time.’ My sense is that many people read that passage as referring to a place called ‘heaven’, where salvation is to be found, and to which we have to go in order to get it. I want to suggest, conversely, that that idea of something being ‘kept in heaven for you’ does not mean that you have to go and live in heaven in order to enjoy it. ‘Heaven’ in the Bible is not usually a reference to a future state, but to God’s dimension of present reality, that dimension which is normally hidden from our gaze but where God’s purposes are stored up. The point is that salvation is being kept safe in heaven for you, in order that it can be brought from heaven to where you are, so that you can enjoy it there. It is rather like a parent, in the run-up to Christmas, assuring a child that ‘there is indeed a present kept safe in the cupboard for you.’ That does not mean that on Christmas Day and thereafter the child is going to have to go and live in the cupboard in order to enjoy the present there. Rather, it means that at the appropriate time the present will be brought forth out of its safe hiding-place, so that it can enrich the life of the child in the world of real life, not just in the cupboardly world.
Wright’s phrase, “where God’s purposes are stored up” makes it sound very much like things in heaven are not yet actual. If this is correct — and I think it broadly is — then the dead who have fallen asleep in Christ, or the souls “under the altar” should not be thought of as enjoying a life in heaven right now, as though that were the eternal reward they were hoping for. They “live to God”, but that means primarily that God has a plan that they shall live again on the earth. In other words, existence in heaven is not the goal, but only the interim or potential stage en route to a resurrected existence on the earth. And the fact that souls in heaven do not have a body is the physical shape of this merely potential existence. True human life is bodily life; the disembodied interim state is not the eternal life to which we all aspire. The resurrection is that life. And the place is the earth.