In Christian theology, patripassianism (as it is referred to in the Western church) or Sabellianism in the Eastern church (also known as modalism, modalistic monarchianism, or modal monarchism) is the nontrinitarian or anti-trinitarian belief that God the Father, Jesus Christ, and the Holy Spirit are three different modes or aspects of one monadic God, as perceived by the believer, rather than three distinct persons within the Godhead - that there are no real or substantial differences between the three, such that there is no substantial identity for the Spirit or the Son.
In the West, this belief was known as patripassianism (from Latin patri- "father" and passio "suffering"), because the teaching required that since the Father had become incarnate in Christ, he had suffered.
From the standpoint of the doctrine of the Trinity—one divine being existing in three persons—patripassianism is considered heretical since "it simply cannot make sense of the New Testament's teaching on the interpersonal relationship of Father, Son, and Spirit." In this patripassianism asserts that God the Father—rather than God the Son—became incarnate and suffered on the cross for humanity's redemption. This not only denies the personhood of God-the-Son (Jesus Christ), but is seen by trinitarians as distorting the spiritual transaction that was taking place at the cross, which the Apostle Paul described as follows: "God [the Father] was reconciling the world to himself in Christ [the Son], not counting people’s sins against them. . . . God [the Father] made him who had no sin [God-the-Son] to be sin for us, so that in him [the Son] we might become the righteousness of God [the Father]." (2 Corinthians 5:19, 21)
It is possible, however, to modify patripassianism so as to acknowledge the Divine Being as having feelings toward, and sharing in the experiences of, both Jesus—whom Christians regard as both human and divine—and other human beings. Full-orbed patripassianism denies Trinitarian distinctions, yet it does not contradict Christianity as defined in the Creeds to say that God feels or experiences things, including nonphysical forms of suffering. With regard to the crucifixion of Jesus, it is consistent with Scriptural teaching to say that God the Father suffered—that is, felt emotional/spiritual pain—along with his Son.