Eph. 6 11, and following; Put on the full armor of God, so that you will be able to stand firm against the schemes of the devil. 12 For our struggle is not against flesh and blood, but against the rulers, against the powers, against the world forces of this darkness, against the spiritual forces of wickedness in the heavenly places. 13 Therefore, take up the full armor of God, so that you will be able to resist in the evil day, and having done everything, to stand firm.…
The simple answer is free will. God has always allowed man to practice free will since Adam. Can murderers be forgiven. Sin is sin to God, He cannot look on it in any form. That is why Jesus came an died for our sins, a sacrifice acceptable for all sin. If one sin can be covered by Jesus sacrifice then all sins are covered. Salvation does not take the gravity of the sin into account, but only the purity of the sacrifice. True repentance is the key to coming under the sacrifice of Jesus. Repentance means to do an about face and walk away from sin, and toward Jesus. God recognizes all who truly repent and follow Christ. Paul the apostle could have been classified as a serial killer before his transformation. If God removed all evil from the world He would be like a child playing with toys. He is an all powerful benevolent Father who loves His children and has provided a way past the sin that those children have chosen. We are all evil, absent the Holy Spirit, and are capable of heinous crimes. Only by His Blood are we healed and welcomed back into the family of Christ. God bless you for writing something that brings up such questions. Remember if there was no war to be fought, why would we need His armor. Mike