Both Eastern and Western Christian traditions usually remember Athanasius of Alexandria as an unwavering defender of the divinity of Jesus Christ, the incarnate Word of God. However, Athanasius was also one of the first writers to argue explicitly for the divinity of the Holy Spirit. In his four Letters to Serapion, Athanasius attempted to present a Scriptural demonstration of the Spirit's divinity. Athanasius' central argument in this enterprise relies on a premise shared with his opponents: the Holy Spirit deifies Christians. Based on this premise, Athanasius argued that the Spirit, by working to deify human beings, must be God—for, Athanasius assumed, only God can deify others. This paper argues that Hebrews 6:4 made three significant contributions to Athanasius' pneumatological arguments in the Letters to Serapion. In Heb 6:4 Athanasius found not only further support for the Spirit's divinity, but also answers to two crucial questions: i) How is it that Christians are deified by the Spirit? ii) How can the Holy Spirit's divinity be distinguished from the 'divinity' of deified Christians? By highlighting the significant role Hebrews 6:4 played in Athanasius' pneumatology, and by observing the concerns and assumptions that Athanasius brought to the text, this paper aims to offer a window into Athanasius' larger exegetical approach, which is an approach that is not uncommon to early Christian interpreters, because it consists of a movement from Christ and the Spirit, to the Scriptures, and then back to Christ and the Spirit. For Athanasius, the Scriptures must be interpreted in light of Christ and the Spirit, yet Christ and the Spirit are also revealed and interpreted by the Scriptures. In this way, the paper shall conclude by highlighting the paradoxical nature of this patristic hermeneutical approach itself.