The Command to worship Allah Alone and rely upon Him
Allah, the Exalted, says to His Messenger, Muhammad , `Say: O mankind! If you are in doubt about the correctness of that which I have been sent with the Hanif (monotheism) religion - the religion which Allah has revealed to me -- then know that I do not worship those whom you worship besides Allah. Rather, I worship Allah alone, ascribing no partners to Him. He is the One Who causes you to die just as He gives you life. Then, unto Him is your final return. If the gods that you call upon are real, I still refuse to worship them. So call upon them and ask them to harm me, and you will see that they can bring no harm or benefit. The only One Who holds the power of harm and benefit in His Hand is Allah alone, Who has no partners.'
In the seventh verse (98), the heedless deniers of truth have been admonished for their failure to make the optimum use of the time of life allowed to them. There was still time for them to leave denial and contumacy. Otherwise, an ominous time was due to come when they will make Taubah but their Taubah will not be accepted. They will say that they believed but their belief will not be welcome. And that time will be the time when the punishment of the Hereafter will appear right before their eyes at the time of death. It was in this connection that an event relating to Sayyidna Yunus (علیہ السلام) and his people was mentioned - that has good counsels and great lessons in it.
The preacher first of all gives his sermon in the language of reason. But if his hearers, even after hearing his arguments remain in doubt, what he must do finally is to express the veracity of his message in sterner language. When a preacher of the Oneness of God tells the polytheists (those who ascribe partners to God): ‘I do not worship that which you worship’ this is not simply a declaration, but an argument in itself. It means: ‘I am also a man like you. I have a mind as you have. Then, why is it that the veracity of something which is understandable to me is not understandable to you?’ If Truth is understandable at the level of one man, it proves that it should be understandable to others also. In spite of this, if others reject it, then it must surely be due to some shortcoming on their part and not to any deficiency in the call to the Truth. If a thing seen by one who has eyes, is not seen by another who likewise has eyes, it simply proves that the latter is not the true possessor of eyes, because it is not possible in this world that a thing which is seen by one person having eyes cannot be seen by another person in spite of his also having eyes.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.