An Accomplished Salvation

What is the difference of the True Gospel and false gospel? What is a progressive salvation? Why do the people of works religion hate the message that the work is done already? How can you be rid of the enemy you live in? Is there anything complicated about the message of the Gospel? Was the Spirit in any of the Old Testament saints? Is the entire Bible from Old Testament to New Testament speaking of the same One? Was there any blood shed before the foundation of the world?