This means that the Lord must bring us through many different kinds of situations and experiences in order to transform us into His image. Jacob is the best example in the Bible of the Lord's transforming work on a person. He wanted the Lord's blessing but he himself was a schemer and a cheat. So the Lord forced him to run away from home to live with his uncle who cheated and mistreated him for 20 years. Even after that Jacob suffered one trial after another but in the end his name was changed from Jacob, which refers to his grasping, cheating nature, to Israel, which means "prince of God". What a transformation!
So, are things such as gossip, slander, misunderstanding, unfair treatment, etc which come our way from Satan? No doubt they are. He is the hidden source of every evil. Does God allow Satan to attack us? Yes He does, because in the end those trials work out for our good. If we stand through the trial, our faith is strengthened by it. On the other hand, if we are defeated by a trial then we begin to lose the sweetness of the Lord's presence and to drift away from Him. Sooner or later, if not in this life time, then in the coming kingdom (I am speaking about defeated believers, not unbelievers.), God will have a way to bring us to repentance and back to himself.
It is similar in the church corporately. Ambition, pride, self seeking, gossip, natural opinions and preferences, etc. give Satan openings to attack. Some may be defeated and leave the church but the church as a whole is purified and strengthened by the trial. A whole group of the Lord's people may go astray but others will need to define the truth more clearly to stand against the error. Without such things the Church would not advance. Satan has been attacking the Church for 2,000 years and causing much damage but within the church, the stronger part, the overcomers, are much closer to fulfilling God's eternal purpose than ever before.