All cults and false religions will add and twist the Gospel message though initially it will not appear as so......, generally after the bait is taken that they do believe in the gospel message..’and’ or ‘but’... is soon to follow with what ever additional “stuff” that group might teach to entrap them in their cult.
In some cases people who have grown “dull of hearing” within the faith begin to desire “something else” or want “more”.....it is not unusual this is when the enemy of mens souls pounces by introducing his bait and switch on the unsuspecting individual.
If they are a person of God's Word they recognize the deception pretty early on......if not...they are “open” to something “new” and or additional to what they already know.
I have seen well grounded Christians take the bait at a low or troublesome time in their life.....the enemy strikes when we're our weakest for the most part. And why many who are, let's say, going thru divorce or a death in the family, or lost relationship, are vulnerable to false teachings because they feel a need "to do something more" to offset the situation. I love the Gospel message just as it is for that door is open to all. When you put "add-ons" in that equation you simply plug up the free flow of live Jesus would have us to live IN HIM...and the walk of "faith" we are positioned by Him to walk.
For 'in the gospel' the righteousness of God is revealed--a righteousness that is by faith from first to last, just as it is written: "The righteous will live by faith.".....Romans 1:17
Tis why the Gospel should be preached every week. If all of Scripture points to Jesus, like are told in the pages of the Bible, it should be easy to do.