The Arabic word
Allah is
the name for the one and only true God who created the whole universe. This word is used by Arabic speakers, both Arab Muslims and Arab Christians.
This word cannot be used to designate anything other than the one true God. The title of the thread is deceptive.
Sahih International
Say, "Call upon Allah or call upon al-Rahman (the Most Merciful).
Whichever [name] you call - to Him belong the best names." And do not recite [too] loudly in your prayer or [too] quietly but seek between that an [intermediate] way.
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Prophet Muhammad is the final prophet of God. It's basic information.
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Kaaba is built by Prophets Ibraheem and Ismael to glorify God. Most of the Arabs had complied with the call of Ishmael (Peace be upon him) , and professed the religion of his father Abraham (Peace be upon him) They had worshipped Allâh, professed His Oneness and followed His religion a long time until they forgot part of what they had been reminded of. However, they still maintained such fundamental beliefs such as monotheism as well as various other aspects of Abraham’s religion, until the time when a chief of Khuza‘a, namely
‘Amr bin Luhai, who was granted unreserved love and obedience by his tribesmen,
came back from a trip to Syria where he saw people worship idols, a phenomenon he approved of and believed it to be righteous since Syria was the locus of Messengers and Scriptures, he
brought with him an idol (Hubal) which he placed in the middle of Al-Ka‘bah and summoned people to worship it. Readily enough,
paganism spread all over Makkah and, thence, to Hijaz, people of Makkah being custodians of not only the Sacred House but the whole Haram as well. A great many idols, bearing different names, were introduced into the area. An idol called ‘Manat’, for instance, was worshipped in a place known as Al-Mushallal. Another, ‘Al-Lat’ in Ta’if, a third, ‘Al-‘Uzza’ in the valley of Nakhlah.
https://islamicnafahat.wordpress.com/2019/03/06/religion-of-arabs-prior-to-islam/https://www.muhammad.net/index.php/biographies/17-ar-raheeq-al-makhtum/605-religions-of-the-arabsLater, when Prophet Muhammad entered it upon opening of Mecca, he smashed all idols and returned it to its pure original state as built by Prophet Ibraheem.
Actually, many Christians pray towards Kaaba:
https://en.qantara.de/content/uncovering-portugal%CA%B9s-islamic-roots-where-christians-pray-facing-mecca