works Athanasius was not a speculative theologian. As he states in his First Letters to Serapion, he held on to "the tradition, teaching, and faith proclaimed by the apostles and guarded by the fathers." He held that both the Son of God and the Holy Spirit are consubstantial with the Father, which had a great deal of influence in the development of later doctrines regarding the Trinity. Athanasius' "Letter Concerning the Decrees of the Council of Nicaea" (De Decretis), is an important historical as well as theological account of the proceedings of that council. Examples of Athanasius' polemical writings against his theological opponents include Orations Against the Arians, his defence of the divinity of the Holy Spirit (Letters to Serapion in the 360s, and On the Holy Spirit), against Macedonianism and On the Incarnation. Athanasius also authored a two-part work, Against the Heathen and The Incarnation of the Word of God. Completed probably early in his life, before the Arian controversy, they constitute the first classic work of developed Orthodox theology. In the first part, Athanasius attacks several pagan practices and beliefs. The second part presents teachings on the redemption. Also in these books, Athanasius put forward the belief, referencing , that the Son of God, the eternal Word (Logos) through whom God created the world, entered that world in human form to lead men back into the harmony from which they had earlier fallen away. His other important works include his Letters to Serapion, which defends the divinity of the Holy Spirit. In a letter to Epictetus of Corinth, Athanasius anticipates future controversies in his defence of the humanity of Christ. In a letter addressed to the monk Dracontius, Athanasius urges him to leave the desert for the more active duties of a bishop. Athanasius also wrote several works of Biblical exegesis, primarily on Old Testament materials. The most important of these is his Epistle to Marcellinus (PG 27:12–45) on how to incorporate psalm-saying into one's spiritual practice. Excerpts remain of his discussions concerning the Book of Genesis, the Song of Solomon, and Psalms. Perhaps his most notable letter was his Festal Letter, written to his Church in Alexandria when he was in exile, as he could not be in their presence. This letter clearly shows his stand that accepting Jesus as the Divine Son of God is not optional but necessary: Biographical and ascetic works His biography of