Contemporary heretical sects or cults all claim to have the proper theological system to replace historic Christianity as the true heir of biblical revelation. They also deny two essential Christian doctrines: the Trinity and salvation as the free gift of God’s grace through faith.1 Why these two in particular? The answer is these two essentials of historic Christianity are inextricably tied together.
It is important to define what historic Christianity means by saying that God is Triune in order to understand how the Lord is uniquely involved in salvation.
The Triune God
The doctrine of the Trinity reflects the Christian belief that God eternally and simultaneously exists as three distinct and distinguishable (though not separate) persons: Father, Son, and Holy Spirit. Not a mere convention of man or of the church, the Bible itself reveals a God who possesses plurality of personhood within the one divine essence (Trinitarian monotheism).2 The one true God has forever been, is now, and shall ever subsist as three distinct persons. None of them came into being or became divine at a given moment in time. God is one in essence or being but three in personhood or subsistence.
Because there is no subordination or inferiority of essence or nature among the members of the Trinity, the three persons are coequal in nature, attributes, and glory. The Trinity sets the Christian concept of God apart from all other alternative views including other monotheistic concepts.
The Trinity and Salvation
So how does the Trinity doctrine impact salvation? One can think of salvation as provided by the three divine persons in three logically ordered steps. First, motivated by agape (self-sacrificing) love, God the Father sends His only begotten Son into the world to save sinners (1 John 4:9–10). So the Father initiates salvation.
Second, God the Son, also known as the Incarnate Lord Jesus Christ, accomplishes our salvation by dying in the place of sinners on the cross. Just before His death Jesus proclaimed His soteriological accomplishment by saying: “It is finished” (John 19:30). So the Son achieves salvation.
Third, God the Holy Spirit, also called the Advocate or Comforter, applies salvation by His threefold work of convicting people of sin (John 16:8), regenerating hearts (Titus 3:5), and enabling people to confess Christ as Lord (1 Corinthians 12:3). So the Holy Spirit employs salvation.
Theologian Michael Reeves explains why salvation is a gift: “It means that this God makes no third party suffer to achieve atonement. The one who dies is the lamb of God, the Son. And it means that nobody but God contributes to the work of salvation: the Father, Son, and Spirit accomplish it all.”3
Why is the Trinity doctrine so important to historic Christianity? Because there is no gift of salvation without it!