Peace of Doubt

Recently I have been dealing with a new paradox of spirit. The Paradox of Peace and Doubt. In D&C 6 the Lord tells us that he will speak peace unto our mind and that this peace is the greatest witness of the Lord. We are told that Satan is the author of contention and the institutor of doubt. However, as I have viewed this I also know that the Devil is cunning and we have been taught that the devil will sell us 9 truths to give us one lie. If this is so wouldn’t the Devil remove opposition once we start to follow him, leaving us with a feeling of peace? And doesn’t the Lord give us doubt to allow us to humble ourselves? So how do we know when the peace is from the Lord or the Devil and how do we know when the doubt and contention is from the Devil or the Lord? How do we know? Does anybody out there know?