One of the oldest and most often-recurring heresies that has confronted the church is modalism. At its core, modalism is an error that denies the diversity within the Godhead. It collapses the distinctions between the three persons of the Godhead, proclaiming that the Father, Son, and Holy Spirit are identical both in essence and in person. In modalism, the Father, the Son, and the Holy Spirit do not exist from all eternity as persons that cannot be confused with one another. Instead, God is like one person who wears different masks or hats. Before the incarnation, the one God was Father. In the incarnation, God took off the Father hat and put on the Son hat. After the resurrection of Christ, God took off the Son hat and put on the Holy Spirit hat. From all eternity, the one God has not existed as three persons in perfect fellowship with one another but as one person in fellowship with no other person, for there was no other person before creation.
Scripture is quite clear, however, that the Godhead has possessed diversity from the beginning. In today’s passage, we read about the Lord God speaking to another Lord (Ps. 110:1). From Jesus’ exposition of this passage in Matthew 22:41–46, we learn that the second Lord mentioned by David in the psalm, who is David’s son, must also be greater than David. His words are an affirmation that the promised Messiah from David’s line precedes and is greater than David’s line. In other words, the Lord to whom David refers is both son of David and Son of God. Psalm 110:1 references the preexistence and deity of Christ. Yet, in the same text we see a clear distinction between the two Lords mentioned. “The LORD” here speaks to a “Lord” who is the Son of God, and the fact that two Lords can speak to one another indicates the presence of two personal relations or subsistences, both of whom are fully God. There is an eternal, personal distinction between God the Son and God the Father (but not in terms of Their essential attributes). In light of the full biblical witness, we may extrapolate this distinction to the person of the Holy Spirit as well, for Scripture in several places refers to all three persons in a manner that assumes distinctions between Them (see Matt. 28:18–20).
This eternal distinction between persons shows us that God is fundamentally personal. From all eternity, because God is three distinct persons, God has enjoyed personal relations. We do not worship an impersonal force but a personal deity who relates to us intimately as creatures made in His image.