22. Spirits, when they have reached a certain degree of purification, are entrusted with missions proportioned to their advancement; they fulfill all those that have been attributed to angels of different orders. God having created from all eternity, it follows that there have been, from all eternity, spirits competent to the discharge of all the duties involved in the government of the universe. A single species of intelligent beings, all alike submitted to the law of progress, suffices to produce the infinite variety of attainment, aptitude, and usefulness. This unity of the creation – in virtue of which all beings have the same starting-point, follow the same road, and raise themselves to higher and higher elevations as the result of their own merits – is far more in accordance with the justice of God than the creation of different species of beings, more or less favored in the way of natural gifts, which would, practically speaking, be the creation of so many privileges.