The doctrine of divine simplicity is thoroughly biblical and central to our worship and devotion to the one, true God of the Bible. An important voice from the past, teaching the necessity of this doctrine to our faith and practice is Petrus van Mastricht (1630–1706), a Dutch theologian whose Theoretical-Practical Theology ( TPT going forward) is considered one of the most comprehensive treatments of Christian doctrine within the Reformed and post-Reformed era. For Mastricht, the doctrine of divine simplicity “discloses to us the foundation of every perfection in God and of every imperfection in the creatures” ( TPT , 2:148). How so? First, where do we see simplicity taught in Scripture? Mastricht lays out the orthodox scriptural arguments, summarized below. God is Spirit (John 4:24), which is immaterial, thus simple. “God is Spirit from himself, and is called Spirit univocally” ( TPT , 2:143). Scripture teaches that God is the absolute first being (Rev