18. From here begins the discourse on the confirmation of Tauhid and the refutation of shirk for these were the actual bases of the conflict between the Prophet (peace be upon him) and the disbelievers of Makkah. The line of argument is this: The whole system of the universe is a clear proof that there is One Allah Who is its Creator, Sovereign, Ruler, and Lord and it is a falsehood that there are many gods who are partners in His Kingdom and Sovereignty, or that there is a Supreme God Who has under Him some minor gods to conduct the affairs of His Kingdom. This proof is also based on the preceding verses in which it has been stated that the universe has not been created as a pastime or a plaything, but for a serious purpose and that there has always been a conflict between the truth and falsehood, and falsehood has always been defeated and destroyed.
19. That is, the angels whom the mushriks of Arabia believed to be the children of God and worshiped them as partners in Godhead.
20. That is, they are engaged in His service day and night without grumbling or ever feeling wearied.