Qur'anic oaths (like any other oath) emphasise the certainty and/or significance of what is being stated after the oath. As for why God is swearing by His created things, it should be noted that in the Qur'an, there is a specific (sometimes metaphorical) connection or similarity between the subject of an oath and the message that follows the oath. From this perspective another function of oaths in the Qur'an is to evidence the message that follows by the use of natural, historical or related phenomena. In other words, in the Qur'an, oaths also serve as evidences for the content of the messages that are followed. For an example, please read the following adapted translation of the explanation of the oath at the beginning of the Surah of Al-Duha from Javed Ghamidi's Al-Bayaan : "By citing the dark night and the bright day as evidence, the Prophet (sws) is assured that just as the material characteristics of this world need the interaction of the night and day for their manifestation, human nature reaches its pinnacle after passing through the test periods of grief and joy. The difficulties he is facing in his mission are only to train and develop him. This does not at all mean that his Lord has abandoned him or is angry with him. He should rest assured that in the coming future he shall succeed in his mission and shall be pleased with the results." - http://www.monthly-renaissance.com As for your second question, there is nothing in Shari'ah that implies swearing by created things is a sin. Whether such swearing has any meaning or significance is of course another issue. Abdullah Rahim March 1, 2005 Answer published by Abdullah Rahim Discussion(s) regarding this Question Further Discussion on Qur'anic Oaths