"Having faith on the Lord; having a hope that ye shall receive eternal life; having the love of God always in your hearts, that ye may be lifted up at the last day and enter into his rest."
Here you have faith, hope and charity (or love). You only have a fraction of the understanding of what faith in the Lord means until you have done as Alma is explaining here. True "faith" which is a principle of power, is acquired by the method Alma is preaching.
Hope that one can receive eternal life is not the vague optimism that it might happen - it is a certitude. You have the promise. You know you will have eternal life. You haven't died and entered into the resurrected state yet. Between the time of the promise and the time you leave this sphere, you have hope. (The way it is used here is defined in Eighteen Verses.)
When God has promised you eternal life then you have "the love of God always in your heart." It is there through the indelible promise He has made. He has changed your status. He has declared through His own voice what great thing you have become. Therefore it is by knowledge alone that such love resides in the heart of man.
This life will end. But you will be raised up. You know when you are lifted up in the last day it will be the power of God that raises you. Such power as God employs to lift a man up confers upon such a person eternal life. The promise alone is a power, conferring the right to lay hold on eternal life when the moment comes. No power in earth or hell can rescind God's word. (D&C 1: 38.) It cannot be done. Therefore, you have knowledge that you will not only be raised from the dead, but "lifted up" as well. Powers, principalities, dominions, exaltations are all promised as yours.
This is how you attain to "rest." It is the "rest of the Lord" as soon as the promise is made by Him. It is His rest when you inherit it in the last day. The words of the promise are enough to guarantee the inheritance. Therefore once the promise is made it is true enough that you have entered into the rest of the Lord. However, until you depart this life, you remain subject to the difficulties of mortality. Graduation is assured, but you must tarry for a little while here.
As one possessing this hope, being filled with faith, hope and charity, it becomes your responsibility to raise up others. Hence the ministry of Alma, and Alma's exposition on the ministry of Melchizedek. God does send true messengers. They can lead you in the way of life and salvation.