"Behold, I send you forth as sheep in the midst of wolves: be ye therefore wise as serpents, and harmless as doves." -Matthew 10:16, KJV

God has sent us into this world to be witnesses for Him. We are to be reaching those around us, but without wisdom, we will fall into the same sin the world is in, reducing our effectiveness for Him. However, if we are not careful, we begin attacking sinners instead of reaching out to help them. This is why God tells us to be as harmless as doves. For example, if a woman is going to get an abortion, the last thing she needs to see is a bunch of picketers. She already knows it is wrong. What she does need is someone who truly cares for her who knows the Bible and can bring her to the Lord and help her through what is already a difficult time. God reached out to sinners--they are already condemned by not trusting Him, so it is our job (as it was His) to help them become justified instead.