Alma 5:41 - 5:45
Alma 5:41 Therefore, if a man bringeth forth good works he hearkeneth unto the voice of the good shepherd, and he doth follow him; but whosoever bringeth forth evil works, the same becometh a child of the devil, for he hearkeneth unto his voice, and doth follow him.
The kind of works a person does is an indication as to whom they are a follower of. If the works are righteous and good, they are following Jesus, the good shepherd. If their works are evil and not so good, then they are following the evil shepherd or the devil.
Alma 5:42 And whosoever doeth this must receive his wages of him; therefore, for his wages he receiveth death, as to things pertaining unto righteousness, being dead unto all good works.
The result is the wages received will be from either the Lord or the devil. If from the devil, it will be removal from all that is good because that is what they wanted.
Alma 5:43 And now, my brethren, I would that ye should hear me, for I speak in the energy of my soul; for behold, I have spoken unto you plainly that ye cannot err, or have spoken according to the commandments of God.
Alma is pleading with them to listen to him and do as he is suggesting. He has tried to speak without ambiguity and to the point so there would be not question as to what he is trying to get across to them. This he has done by way of commandment.
Alma 5:44 For I am called to speak after this manner, according to the holy order of God, which is in Christ Jesus; yea, I am commanded to stand and testify unto this people the things which have been spoken by our fathers concerning the things which are to come.
Because he has the priesthood and a commandment from God to speak to the people of Zarahemla, he is doing so. He has been strictly charged talk about what has been prophesied in their scriptures and to tell what will happen to the people if they do not repent quickly.
Alma 5:45 And this is not all. Do ye not suppose that I know of these things myself? Behold, I testify unto you that I do know that these things whereof I have spoken are true. And how do ye suppose that I know of their surety?
What he is telling the people is not from his personal philosophy and observation. These topics he knows to be absolutely true and asked his listeners how do he know that?