To "wrest" means to apply such twisted reasoning that the philosophies of men are mingled with scriptures so that the result is error.
The object of the scriptures is to make matters "plain" and prevent people from "erring" in their effort to follow God.
What is the difference between someone who with their scriptures before them, finds their message sufficiently "plain" and "understood" that they "cannot err," and someone who has the same set of scriptures and engages in "iniquity" and "abominations" because of their false religious ideas? How can someone who is religious be certain they are not among those who err, but is instead among those who find holiness and develop faith to repent?
So, applying Alma's teaching to us, we should ask ourselves if we have repented? If we have received a message from angels declaring glad tidings? If we have received what we would recognize as a message from the Lord by someone declaring repentance? Or do we have a weak tradition which assures us that we are right, while letting us entertain abominable (false, religious-based) errors in our beliefs?
Powerful teachings from Alma. But then again, one should expect nothing less from a true messenger bearing a holy order of power and authority after the order of the Son of God. A weak and vacillating voice telling us all is well and we're going to be fine just seems wrong by comparison. At least I would think so.