We have been asked to explain Isaiah 45:7 as it pertains to God as the creator of evil. 
The querist wonders how this can be the case, in light of God’s love and purity.
The passage from Isaiah reads as follows: 

"I form the light, and create darkness: I make peace, and create evil: 

I the Lord do all these things."

In context, God is speaking through Isaiah concerning Cyrus, the Medo-Persian king who more than one hundred years later was to capture Babylon because of the grievous sins of that infamous city. The intent of Isaiah’s prophecy surrounding verse seven is to make it clear beforehand that God, and not Cyrus, would be the ultimate cause of Babylon’s fall and Judah’s deliverance. Cyrus would be but an agent working in heaven’s behalf to fulfill divine retribution.

The word "evil" in scripture may refer to sin, to sin’s punishment, or to other various misfortunes. We know that God is not the source or cause of sin, for James 1:13 instructs, "Let no man say when is he tempted, I am tempted of God: for God cannot be tempted with evil, neither tempteth he any man."

 From the earliest days of man’s existence, Satan – not God–has been the culprit in back of all sinful evil (Gen. 3; Jn. 8:44; I Pet. 5:8).

The God of heaven, however, has always been concerned with divine punishment and retribution. "Shall there be evil in a city, and the Lord hath not done it?" (Amos 3:6).  

Throughout history, God has often made use of a sinful nation or individual in bringing punishment upon the iniquities of other nations. The Israelites were defeated, for example, at the hand of the Philistines as recorded in I Samuel 4; yet inspiration credits God with having smitten His people (I Sam. 4:3).

In short, the evil which God is said to create in Isaiah 45:7 is not sin, or common misfortune, 
but rather divine punishment. 
In this case, heaven’s retribution is to be meted out upon sinful Babylon 
through the agent of Cyrus at the helm of the Medo-Persian army.