Our difference is not because of Jesus, it is because Tawheed(Islamic Monotheism).
what is Tawheed?
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what is the meaning of “Tawheed”?
Tawheed is based from the root word Wah-hada. Wahhada means to make something one. Tawheed is the act of ascribing unity to something. (this is the linguistic definition).
When it comes to islamic sciences - Tawheed refers to the unification of Allah(subhana wa ta'ala) in the aspect of Rububeeyah, Ulooheeyah and Asma wassiffat. To make Allah(subhana wa ta'ala) one in these 3 aspects.
Tawheed ar-Rububeeyah = its based on Qur'an and sunnah, meaning Allah (subhana wata'ala) is one. It means to acknowledge that Allah (subhana wata'ala) is the only one who sustains, controls and created all the mankind and the worlds. In other words the fact that we have only creator, one sustainer, one who in control of all our affairs is Tawheed ar-Rububeeyah. It comes from the root word Rubb. (linguistic meanings – owner, leader, caretaker)
Tawheed al-Ulooheeyah = Tawheed of worship. This the natural follow up of Tawheed ar-Rububeeyah. Once we have acknowledged that Allah(subhana wa ta'ala) is our creator, in other words we have acknowledged Tawheed ar-Rububeeyah, we reach the understanding that we have to worship that creator.
Tawheed al-Asma was siffat (names and attributes) = Natural follow up of Ulooheeyah.
Allah(subhana wa ta'ala) has perfect attributes which belongs only to Allah(subhana wa ta'ala). We say that every negative attribute does not belong to Allah(subhana wa ta'ala). Example Allah (subhana wata'ala) is Ar Rahmaan.
Most of mankind accepts Tawheed ar-Rububeeyah. If we go to a Christian and ask them “Who created you ?” they will say they "God the father". Even Hindus and Jews agree that there is one main God. Only a few groups deny Tawheed-ar-Rububeeyah. This Tawheed is engraved in the very nature of Man. Atheism has always been a minority. which is the opposite of this type of Tawheed. One religion who actually believed that there were 2 God's are the Zoroastrians (Parsi's - fire worshipers), The believe that there is a God of good and God of bad. They go against Tawheed ar-Rububeeyah.
Tawheed al-Ulooheeyah is where the majority of mankind went astray. If you ask the Christians “Who created you ?” they will say “God the father”, but if you ask them who do you ask from they will say Jesus. This is where the most mankind goes wrong. They worship other than Allah(subhana wa ta'ala) which automatically makes them in error or Tawheed al Asma was siffat. Meaning that they give attributes which belong only to Allah(subhana wa ta'ala) to which ever they worship, which is Shirk (Associating partners)
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Narrated Ubadah bin As-Samit ( R.A) that Allah's Messenger ( saw) said:
"Whoever testifies that there is nothing worthy of worship in truth ( no GOD) except Allah Alone, Who is without ( peer or) partner , and that Muhmmad is His slave and Messenger, and 'Iesa( Jesus) is the slave of Allah, His Messenger, and His word which He bestowed in Maryam( Mary) and a spirit ( created) from Him , andthat Paradise & Hell-fire are realities, Alah will admit him into Paradise, whatever hisdeds might be." ( Sahih Al- Bukhari, Hadeeth No. 3253)
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So as you can see the difference between Christianity and Islam is Monotheism, that we Muslims stay firm on the stance of Tawheed and reject every sort of Man-God worship which christians are upon weather they are worshipping Jesus, or Pope John, or Pual, or even Prophet Muhammad.
Because everything which a person worships besides the creator is Shirk(Polytheism).
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Allah the Almighty said:
“ Verily , Allah forgives not that partners should be set up with Him in worship, but He forgives except that ( anything else) to whom He pleases.” ( 4:48,116)
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Surah 5:72 Surely, they have disbelieved who say: "Allah is the Messiah (Iesa (Jesus)), son of Maryam (Mary)." But the Messiah (Iesa (Jesus)) said: "O Children of Israel! Worship Allah, my Lord and your Lord." Verily, whosoever sets up partners in worship with Allah, then Allah has forbidden Paradise for him, and the Fire will be his abode. And for the Zalimoon (polytheists and wrongdoers) there are no helpers.
73 Surely, disbelievers are those who said: "Allah is the third of the three (in a Trinity)." But there is no ilah (god) (none who has the right to be worshipped) but One Ilah (God -Allah). And if they cease not from what they say, verily, a painful torment will befall the disbelievers among them.
74 Will they not repent to Allah and ask His Forgiveness? For Allah is OftForgiving, Most Merciful.
75 The Messiah (Iesa (Jesus)), son of Maryam (Mary), was no more than a Messenger; many were the Messengers that passed away before him. His mother (Maryam (Mary)) was a Siddiqah (i.e. she believed in the words of Allah and His Books (see Verse 66:12)). They both used to eat food (as any other human being, while Allah does not eat). Look how We make the Ayat (proofs, evidences, verses, lessons, signs, revelations, etc.) clear to them, yet look how they are deluded away (from the truth).
76 Say (O Muhammad SAW to mankind): "How do you worship besides Allah something which has no power either to harm or to benefit you? But it is Allah Who is the AllHearer, AllKnower."
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So as you can see christians deny that the creator should be worshipped alone but they worship Jesus a creation because they believe they will "get" Interseccion". This is the same thing which the Pagan Arabs used to do. They believed in Allah but they made Idols and set up Angels for worship because they "believed" they will help them get closer to Allah and make "Interseccion" on their Behalf. And All of these Paganistic Acts are rejected by Islam.