All divine books including the EverGlorious Qur'an i.e. the Last Divine Message, call for Tawhid and devoting `Ibadah to Allah Alone, obeying His Commands and avoiding His Prohibitions.
Similarly, all messengers call for Tawhid, obeying the Commands of Allah, giving up what He Prohibited, following His Shari`ah (Law) and keeping away from whatever He prohibited.
All Mukallafs (persons meeting the conditions to be held legally accountable for their actions) of mankind, Jinn, Arabs, nonArabs, men and women should worship Allah Alone and follow what Prophet Muhammad (peace be upon him), did or said by observing what he did and abandoning what he quit. The essence of Din is to testify that there is no god but Allah and that Muhammad is the Messenger of Allah.
This is the essence of `Ibadah, to worship Allah Alone, by means of Du`a' (supplication), hope, fear, vow, sacrifice and other acts of worship.
And your Lord has decreed that you worship none but Him. And that you be dutiful to your parents.
You (Alone) we worship, and You (Alone) we ask for help (for each and everything).
And they were commanded not, but that they should worship Allâh, and worship none but Him Alone (abstaining from ascribing partners to Him)
Say (O Muhammad ﺻﻠﻰ ﺍﷲ ﻋﻠﻴﻪ ﻭﺳﻠﻢ): "Verily, my Salât (prayer), my sacrifice, my living, and my dying are for Allâh, the Lord of the 'Alamîn (mankind, jinn and all that exists). "He has no partner. And of this I have been commanded, and I am the first of the Muslims."
Verily, We have granted you (O Muhammad ﺻﻠﻰ ﺍﷲ ﻋﻠﻴﻪ ﻭﺳﻠﻢ) AlKauthar (a river in Paradise). Therefore turn in prayer to your Lord and sacrifice (to Him only).
`Ibadah is the right of Allah Alone; it does not fit for a close angel, sent prophet, idol, Jinn or anything else. It is Allah's Right Alone, whom Alone one should worship, invoke, hope, fear, offer sacrifices, vows, Salah (prayer), Sawm (fast), Hajj and Sadaqah (voluntary charity), and so on. Allah (Glorified be He) is truly worthy of being worshipped and others are falsely worshipped.
That is because Allâh — He is the Truth (the only True God of all that exists, Who has no partners or rivals with Him), and what they (the polytheists) invoke besides Him, it is Bâtil (falsehood).
When Prophet Muhammad (peace be upon him) was sent, all the Arabs and other nations save a few were observing Shirk (associating others with Allah in His Divinity or worship), some would worship angels, prophets, idols, statutes, trees, stones, graves and stars and seek their help and make vows to them. Allah sent the great Prophet Muhammad (peace be upon him) to call them to Tawhid and warn them against the grave consequences of Shirk.
He (peace be upon him) did that as due; he called for Allah and guided to His Din, which He has chosen for people. He taught people Tawhid.
He (peace be upon him) stayed in Makkah for thirteen years, calling for Tawhid, devoting `Ibadah to Allah, and abandoning worshipping anything else. After ten years, Allah made obligatory on him the five daily prayers before he would immigrate, when he was taken during the Isra' (Night Journey) to Bayt AlMaqdis (Jerusalem) and then ascended to the heaven, went beyond the Seven Heavens, was raised above that and Allah (Glorified and Exalted be He) spoke to him and revealed to him the five daily prayers which he (peace be upon him) taught people and which Muslims performed in Makkah. The Prophet (may Allah's Peace and Blessings be upon him) then immigrated to Madinah where Allah obligated other religious matters such as Zakah (obligatory charity), Sawm, and Hajj.