XI. (10) Their theory that souls have a previous existence before entering man refuted.
Under the tenth head they are reported as asserting that the souls which are placed in men's bodies have previously been without body and have sinned in their heavenly habitation, and for this reason having fallen from their high estate to a lower one alight upon ruling spirits of various qualities, and after passing through a succession of powers of the air and stars, some fiercer, some milder, are enclosed in bodies of different sorts and conditions, so that whatever variety and inequality is meted out to us in this life, seems the result of previous causes.
This blasphemous fable they have woven for themselves out of many persons' errors: but all of them the Catholic Faith cuts off from union with its body, persistently and truthfully proclaiming that men's souls did not exist until they were breathed into their bodies, and that they were not there implanted by any other than God, who is the creator both of the souls and of the bodies. And because through the transgression of the first man the whole stock of the human race was tainted, no one can be set free from the state of the old Adam save through Christ's sacrament of baptism, in which there are no distinctions between the re-born, as says the Apostle: “For as many of you as were baptized in Christ did put on Christ: there is neither Jew nor Greek: there is neither bond nor free: there is neither male nor female: for you are all one in Christ Jesus.”
What then have the course of the stars to do with it, or the devices of destiny? What the changing state of mundane things and their restless diversity? Behold how the grace of God makes all these unequals equal, who, whatever their labours in this life, if they abide faithful, cannot be wretched, for they can say with the Apostle in every trial: “who shall separate us from the love of Christ? Shall tribulation, or distress, or persecution, or famine, or nakedness, or peril, or sword?
As it is written, 'For your sake we are killed all the day long, we are accounted as sheep for the slaughter.' But in all these things we overcome through Him that loved us.” And therefore the Church, which is the body of Christ, has no fear about the inequalities of the world, because she has no desire for temporal goods: nor does she dread being overwhelmed by the empty threats of destiny, for she knows she is strengthened by patience in tribulations.
Source: Letters (New Advent)