(Oh Nabi) surely we have sent you as a witness (present and seeing) and as a bearer of glad-tidings (of our mercy) and a timely Warner (against the torment). In order that you (Oh people!) may believe in Allah and his Apostle, and may assist him, and honour and respect him heart and soul. And that you may sanctify and glorify Allah morning and evening
Hazrat Qadi Iyaad alaihi Rahmah states:
Allah Taala has made it an essential and a necessary act to respect the Prophet , and compulsory to obey him (Shifa Sharif)
Meaning that from the verse the command to obey the Prophet (Sallallahu Alaihi wa Sallam)and respect him is imperative, compulsory and not just permissible. Therefore is it obligatory upon the Muslims to obey and have respect for the Prophet (Sallallahu Alaihi wa Sallam) in someway or another. We also get to know from the verse that there is no specific or particular way in respecting the Prophet (Sallallahu Alaihi wa Sallam)therefore; we should respect him in every way. However to call the Noble Prophet Sallalaho alaihi wasallam as God or as a Son of God is Kufr and that person becomes an infidel and is out of the boundaries of Islam.
In the above verse, Imaan has been mentioned first (In order that you (Oh people!) May believe in Allah and his Apostle) then the respect of the Prophet (Sallallahu Alaihi wa Sallam) has been mentioned (and may assist him, and honour and respect him heart and soul), and then the command of worship (And that you may sanctify and glorify Allah morning and evening). So we get this image that without Imaan the respect of the Prophet (Sallallahu Alaihi wa Sallam)is useless, and without the respect of the Blessed and holy Messenger Sallalaho alaihi wasallam, all our worships, like Salaah, Zakaah, Sawm, Hajj and the rest, are invalid and unaccepted.
In another place Allah, Taala says:
And who so respects the Signs of Allah, then this respect is because of the piety in their hearts
The summary of this ayah is that people who have fear of Allah in their hearts, then they are the ones who will respect the Signs of Allah. The Signs here means by the signs of Allahs religion, Islam. (Tafsir-e-Jalalain).
Moreover, the Prophet (Sallallahu Alaihi wa Sallam)is the greatest sign of Islam and is the highest and supreme sign of the religion. Those who deny the respecting of the Prophet , even though they look like good practising Muslims, their hearts are barren and empty with the fear of Allah!
It is in the Quraan: