Heaven is chiefly and substantially the supernatural state on the other side of death. We must not press figurative language so far as to think of heaven as an enclosed space into which any one, good or bad, could enter, whether qualified or not. Heavenly beatitude involves two things: subjectively, an aptitude for God; objectively, the unveiled presence of God, so as to be seen and possessed by man in the risen state. The presence of God would be a torment worse than hell to the soul in which the aptitude for Him had not been developed. Beings which have not that aptitude formed by grace and virtue in the state of probation, such as inanimate objects, beasts, and sinners, are not capable of enjoying the delights of heaven. Those who have that aptitude are in heaven. The Guardian Angels, so far as they are in place, are on this earth; yet they are not, for that, outside of heaven (Matt, xviii. 10). The throne of God is situated only in boundless immensity. To be in heaven is a matter of internal aptitudes and not of geographical locality, like being in the grace of God or in the Church. These aptitudes can only be formed in the soul by supernatural life while on earth. Failing this, the unrepentant soul cannot enter heaven; God could not admit it to the enjoyment of heaven, being what it is, for this would be a contradiction in terms. That which harmonizes with the spiritual condition of the blessed and constitutes their supreme joy, is repugnant to the formed habits and tastes of the wicked, and so would excite their antipathy and inflict pain upon them. You must spiritualize yourself during this life, else you will remain forever unapt for heaven.
