Hamzah Yusuf
Tau’heed references monotheism. Shirk references polytheism.
Definitions: https://dictionary.cambridge.org/dictionary/english
Monotheism: the belief that there is only one god.
Polytheism: belief in many different gods.
One: a single thing; not two or more.
Tri: three.
Conclusion: The belief in more than one god constitutes polytheism, i.e., shirk, and, those who have this belief system are polytheistic, i.e., mushrikun.
Shirk refers to taking others as gods or lords besides Allah, as clearly indicated in ayah 9:31, as well as, its explanation found in the Prophet’s statement to Adi Ibn Hatim. By definition, those who believe in multiple gods, are mushrikun.
Hamzah Yusuf seems to toy with the concept of trinity: “Christians believe God is One, they do not believe God is three. They really do not. They do believe God is three, He is One but He is tripart in this mystical mysterious way and they will never explain it and they believe in One God. They are not idolaters like that, they believe in one God.”
So, which one is it? Do “Christians believe God is One,” or, “They do believe God is three “? To Christians, is God one person or three persons?
Christians believe in the formula of 1+1+1=1. However, they state that God is one-in-three and three-in-one. So, they acknowledge the fact that 1+1+1=3, in that there are three different persons incorporated into the God-Head. Christians call this creed ‘Trinity.’ They confirm that their creed is based on three gods: TRI-nity.
Allah said in the Quran that Christians believe in three, {O, People of the Scripture (Christians)! Do not exceed the limits in your religion, nor say of Allâh aught but the truth. The Messiah ‘Îsâ (Jesus), son of Maryam (Mary), was (no more than) a Messenger of Allâh and His Word, (“Be!” — and he was) which He bestowed on Maryam (Mary) and a spirit (Rûh) created by Him; so, believe in Allâh and His Messengers. Say not: “Three (Trinity)!” Cease! (It is) better for you. For Allâh is (the only) One Ilâh (‘God’), glory is to Him (Far Exalted is He) above having a son.} (4:171)
Note how in ayah 4:171, Allah didn’t say, “Do not say, ‘Three in one and one in three.” He said “three” and followed this term by stating that {Allâh is One Ilâh (‘God’)}. Thus, ‘three’ in the ayah means, three alihah (gods). By claiming that Allah is three in trinity, Christians are calling the other two persons in the trinity as alihah besides Allah.
In addition, Allah called Christian creed ‘shirk’ in ayah 9:31. This is because their creed is based on worshipping multiple gods. Let’s be clear, Christians worship an angel, the Holy Ghost, who they appointed as being god. Also, Christians worship a human being like them, Jesus, who -to them- is also god, but who used to eat, sleep, and answer the call of nature. How can this possibly not be shirk? To continue, “Trinity Godhead is ever confusing. Here we [allegedly] have one God, but three persons. They are united in divine nature and qualities, but divided in action and even fate. For instance, the job of the Father is different from the job of the Son and the Holy Ghost. Christians assign to each of these personalities different roles, [different] decisions, [different] actions, [different] presence, and, [different] consequences of actions and decisions. To explain, the Son-God is the one who transformed into a man, who lived a human life. This description is not given to the Father or the Holy Ghost, because they did not incarnate as the Son did. When the Son died, he gave up the Holy Ghost, not the Father. If Christians were asked about who among the three became a man, they will not say it was the Father or the Holy Ghost, only the Son. If Christians are asked about who gave up the other, the Holy Ghost or Jesus, they will not say it was the Holy Ghost, but Jesus. Therefore, Trinitarian Christians assign different roles and different actions to each member of the Triune Council. Yet, they somehow consider the three to be in perfect harmony, then claim that ‘It has to be stated emphatically that Christians do not worship three gods but one God.’ However, Christians worship three divine beings, three different partners, three different personalities, three different manifestations, i.e., three different gods.” (Jalal Abualrub. Christian-Muslim Dialogue, Pg., 50-1)