The people had questioned why the Lord would only send one man to them, but now with Amulek being with Alma, there are two witnesses and this fulfills the law of witnesses which says that everything will be established by the mouths of two or three witnesses. Alma then talks about the authority of the priesthood explaining that all men who hold the priesthood were foreordained prior to this life. He uses the words "from the foundation of the world" meaning from the very beginning. Men who hold the priesthood were foreordained at that time because of their "exceeding faith and good works; in the first place being left to choose good or evil; therefore they having chosen good, and exercising exceedingly great faith are called with a holy calling." However, he makes this interesting statement, "others would reject the Spirit of God on account of the hardness of their hearts and blindness of their minds, while, if it had not been for this they have might have had as great privilege as their brethren." I think this means two possible things. One is that there are some who were foreordained but reject the gospel in this life and never enjoy the blessings of exercising the priesthood. I think the other meaning is there are some who were foreordained before this life, ordained in this life, but never enjoy the blessings of the priesthood they hold because of the attitudes they have and the actions of their lives.
There are four things involved when men are called of God. One is they must be called by prophecy. This means they are called by revelation, by the power of the Holy Ghost. Both the person doing the calling and the person receiving the priesthood must be in tune with the Spirit. Two, there must be the laying on of hands. This allows that more than one person supports the calling as men unitedly lay their hands upon the head of the recipient and convey the authority. Three, the ordained person must have divine approval meaning that what he does is the mind and will of the Lord, it is his doctrine. And four, they administer the ordinances in the place of the Lord, with his approval. These four things must be a part of every priesthood holder's ordination and practice of the priesthood.
When a person exercises the priesthood in righteousness and humility, the power of the priesthood is evident and it is a witness of not only the truth of the gospel, but a witness that the Lord cares enough about his people to do all that he can for them to have the truth and the blessings of his gospel in the same manner the Lord would give it were he here. It is unfortunate that so many fall far short in both how they hold and exercise the priesthood. As Section 121 of the Doctrine and Covenants states, the rights of the priesthood are connected to the powers of heaven and are inseparable. And if a man is in sin, uses his authority to gratify his pride, or uses it to for power and control, the powers of heaven are withdrawn and the man actually loses his priesthood authority. Such people are like those Alma talked about when he says, if it had not been for this they have might have had as great privilege as their brethren. The evidences that a person has the authority of the priesthood is he uses gentle persuasion, he is long-suffering, gentle, meek, and filled with unfeigned (not pretended) love. He is kind, is interested in only the truth and is without hypocrisy or guile (has no deceptive motives). This is a tall order for any priesthood holder and I know from personal experience that priesthood holders for the most part are a work in progress.