The aim of this article is to show that the concept of substance in the philosophy of Spinoza and Hegel can also be used to mean the concept of God. This means that both philosophers can be read as theists. While Spinoza understands from the concept of substance that which is in itself and can be grasped through itself, Hegel understands that in which all reality gains its existence and permanence. In this context, firstly, the geometric axiomatic method used by Spinoza and Hegel's speculative dialectic method will be explained and the differences between them will be determined. Subsequently, Spinoza's and Hegel's understandings of substance will be detailed. The concept of causa sui in Spinoza, the claim that things are in God but not God, and his distinction between Natura naturata and Natura naturans will be discussed. Hegel interprets God as encompassing everything that is absolute reality in himself and for himself, and bases the historical process of the mind on the belief that God is embodied in the body of Jesus, which is one of the Christian doctrines. For these reasons, it will be argued that both philosophers can be read as representatives of process theism.