3 great points made by Greg Boyd:

1. Some people use this verse to say that God is sometimes the source of evil but we must look at the entire Bible and note that based on what the Bible says about God being good, this verse is the exception and not the rule
2. There are unseen evil forces at work
3. the original Greek of this text  states: “…But let the works of God be displayed in him…”  Therefore it does not say that God caused the man to be blind but his blindness lead to God’s goodness being displayed