Response to your question is as follows:

In the Christian understanding of the Holy Trinity, God is presented as a single being who manifests in three persons: the Father, the Son, and the Holy Spirit.

The Christian Trinity versus Islamic Monotheism: A Comparative View

Response to your question is as follows:

In the Christian understanding of the Holy Trinity, God is presented as a single being who manifests in three persons: the Father, the Son, and the Holy Spirit. This doctrine implies that although there appear to be three, they are one in essence and action. For example, one source states:
"The name of the incarnate God is Jesus Christ. This is proclaimed to us by the Revelation of God—the Holy Scripture, the Bible. But not only that, but also that God, being One in essence, is Triune in Persons. ... Through this, God is instilled into the human soul; the Holy Spirit connects us with Christ and His Father so that God becomes our life. And not only in anticipation of posthumous bliss, but even here on earth we attain the fullness of existence in the One Tri-Personal God. This, very briefly, is the essence of Christianity."
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An additional explanation emphasizes the unity of God expressed through three hypostases:
"The same God exists as three in hypostases and one in the unity of essence and nature. Thus our Lord Jesus Christ, the Only-Begotten Son of the Father, revealed to us that this very Son along with the Father and the Spirit are one in essence, consubstantial and co-eternal..."
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In contrast, Islam strictly rejects the idea of the Trinity because it contradicts the principle of absolute monotheism (tawhid). Islam asserts that Allah is one, and none of His “persons” or composite elements can imply a multiplicity in the essence of God. For instance, one cited excerpt explains:
"In Islam it is categorically denied that Jesus is God or the Son of God: 'Those who claim that Jesus, the son of Mary, is God do not believe... How repulsive they are!'"
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Furthermore, the polemic with Christian dogmas continues:
"In other places, the Quran even more vividly presents a polemic with the main Christian dogmas about God—the Trinity and the Incarnation: ... So believe in Allah and His messengers, and do not say 'three'! Abstain, for it is better for you; indeed, Allah is the one and only God. Exalted is He above having a child."
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Thus, Christianity interprets the Holy Trinity as three interrelated yet united persons in one God, through which salvation and communion with believers are achieved. In turn, Islam adheres to the idea of the absolute unity of God (Allah) and categorically rejects any interpretation that equates Jesus or the Holy Spirit with a part of the Divinity, considering such representations mistaken and contrary to the principle of monotheism.