Satan still accuses the brethren before God. He will be cast down sooner or later. If you want the full picture on the overcomers, read "God's plan and the overcomers" by Watchman Nee.
Satan accuses us because he can attack our conscience, which is a faculty of the spirit. When have a guilty conscience, we are weak because our spirit man is where our strength lies. To overcome, we need to first plead guilty then confess the forgiveness that is ours through the blood of Christ. We testify to the forgiveness that is ours. There is no glory to God if we wallow in self pity and continually focus on sin. Too many Chritians live in defeat because they are ignorant of the victory belongs to us. Yes, we need to know that nothing good dwells in us. We also need to know and express that we are new creations in Christ Jesus.