In order to ascertain God's perfect will, we must be transformed by the renewing of our minds per Romans 12:2. The spiritual battle for our eternal destinies begins with the battle of our thought lives.
We are to guard what remains in our minds. We have authority over our thought life.
We are to test all things. (1 Thes. 5:21) We are to test the spirits. (1 John 4:1)
We are to take every thought captive to make them obey Christ. (1Cor. 10:3-5)
The indispensable weapon is that of spiritual discernment. It is a gift of the Holy Spirit. (1Cor.12:10)