Sorry for the quick finger.
The Athanasian Creed was established to expressly reject Modalsim in the church.
Modlaism is the separating of the triune God into individual person.
Modalism allows for worship (love) of each person of the Godhead, individually, as sufficient for salvation.
Each person then performs only one activity of Salvation.
Modalism is a heresy as old at Matthew 28:19.