In Books 6-10 Origen carries through to completion his program, begun in Books 1-5. of defending human freedom and of opposing the natural predestinarian doctrine of the sects founded by the Gnostic heretics Marcion, Valentinus, and Basilides. These schools relied heavily on texts from Paul, interpreted in isolation from the rest of Scripture, not only to deny free will but to support the doctrine that salvation is determined by the nature one receives at birth, whether good or evil. In contrast Origen clarifies passages in Romans by citations from Paul's other letters, from the Gospels, and from the Old Testament. He attempts to construct a coherent and unified "biblical theology." Ori