To understand the Trinity properly, it is necessary to observe that the Bible reveals one God and not three. The Old Testament Scriptures affirm this reality from the opening line (Gen 1:1). The Ten Commandments likewise open this way, “I am the Lord your God … you shall have no other gods before Me” (Exod 20:2-3). Furthermore, the central command of all Scripture, called the shema, rests squarely on this monotheistic reality, which Jesus repeated centuries later in his public teaching ministry (Deut 6:4; cf. Mark 12:29, Luke 10:27). At the outset of the church era, James reaffirms this monotheistic belief in one God for the church (Jam 2:19), and Paul also draws attention to this timeless doctrine (1 Cor 8:4-6).

To understand the Trinity properly, it is necessary to observe that the Bible reveals one God and not three.

That God is one seems to reveal more than the singular number of God, for it also relates to his divine essence and his unity of purpose. Divine essence refers to all that being the one, true God requires. It refers to all the qualities (and the extent and proportion of those qualities) that are essential to being God (hence, “essence” as in “essential”). As such, he perfectly embodies all the necessary attributes of God, and this divine essence is unchangeable and indivisible. Many theologians call this the doctrine of simplicity, meaning that the nature of God cannot be divided into parts. So, he is always God and perfectly God in every way. In that sense he is one. He is also one with regards to his unity of purpose, which refers to the mutual harmony of the three persons within the Godhead. Neither the Father, nor the Son, nor the Holy Spirit ever functions independently, or out of harmony with one another, or out of harmony with the singular, shared will of the Godhead (John 5:19; 8:28; 12:49; 14:10).