This means that some of Allah’s (swt) creatures are evil, even though they have some goodness. As everything in this existence is nor pure good neither completely evil, for, one of its side could be good and another one could be evil. Allah (swt) is teaching us to seek refuge from evil so we could keep the good sides nd seeking refuge is in Him (swt) only because He is the Only One capable to protect us from all the evils.