The enthusiasm leads to the idolatry

[selfsame]

The exaggeration in loving the Christ, the Christian saints, Jewish sages, Muslim imams
leads to --> the enthusiasm which leads --> to glorifying these persons like God's glorifying, which will lead to --> the idolatry (or associating these figures with God in the glorification and worship

which is contrary to the first and the most important commandment: that is to worship God alone and to take none apart of God in the worship and glorification

Quran 4: 171, which means

[God – be glorified – addressed Christians]

(171. People of the Book [: the Gospel], do not exaggerate in your religion nor say aught concerning God save the truth

The Messiah: Jesus the son of Mary was but a messenger of God, and His "word", that He cast to Mary and a "spirit" [coming] from His [neighborhood

so believe in God and [all] His messeng

Say not "Trinity"; desist [from such words], it will be better for you; for God is One God; Far Exalted is He above having any son

To Him belong all the [cosmic destructive factors] in the [gaseous] heavens, and [the sudden destructive factors] on earth

God suffices for a One Who records your acts

More explanation of this great aya is in the link
http://quran-ayat.com/pret/4.htm#a4_171

[selfsame]

Then God - be glorified - gave more proofs and arguments against considering Jesus as a god or a son of God or one part of a Trinity, so He said in the following aya

Quran 4: 172, which means
The Christ will never disdain to be a servant of God, neither will the angels favored [by God

Whosoever disdains to serve Him, and waxes proud, He will gather them altogether to Him [in the space

More explanation is in the link
http://quran-ayat.com/pret/4.htm#a4_172

===============================================

Afterwards, God - be glorified - explained what He will do to "the submissive" and "the disdainful"

Quran 4: 173, which means
As for those who believe and do righteous [deeds], He will give them their [due] wages, and increase them still more out of His bounty

Whereas those who are disdainful and arrogant, He will punish them [in Hell] with a painful chastisement, and they shall not find for them, apart from God, any guardian or savior

More explanation is in the link
http://quran-ayat.com/pret/4.htm#a4_172