Angels declared it to the shepherds near Bethlehem. (Luke 2: 8-15.) Alma expected a similar announcement.
"We only wait to hear the joyful news." He EXPECTED the news to be shared. He knew they would have the announcement. He EXPECTED the angels to declare the arrival. He knew heaven would not leave these people without a herald of the news.
Imagine that. A prophet confident that the Lord will do nothing without first making known to the people His secrets! (Amos 3: 7.) It is one thing to teach this concept. It is another to live it. Alma is living it. Therefore angels did come and did make things known to him.
What does it take to have faith like this?
If you do not possess this kind of faith, can you be saved? Moroni taught that the absence of such faith condemns the people who no longer have such things happening among them. (Moroni 7: 36-37.)
Do we expect the Lord to tell US about things by the mouth of angels before they happen? Or do we expect the Lord will tell someone inside the bowels of an organization, and we will get some announcement through the prescribed channels, thereby relieving us from obtaining the ministry of angels? Then why is the visitation of angels an Aaronic (lowest) priesthood key? (D&C 84: 26.) This is the right of young people beginning at age 12, mind you. Should we expect the angelic heralds to come to everyone, 12 year of age or older? Why or why not?
Alma knows it will happen. But he does not know when it will happen. He would like it to have been in his day. It was not. But whether it was to happen in his life or afterwards, he nonetheless had faith, knew angels, awaited the message, and rejoiced at the idea of His coming.
How meek! How faithful! No wonder such a man possessed and knew the details of this holy order from God. No wonder he could teach with authority about it. How great the lesson he has left for any who will take seriously the message he taught.
Faith of this sort should be the common heritage of the Lord's people. It was never intended that an elite, distant hierarchy would be put between God and His people. If you are His, then you should KNOW Him. If you do not know Him, then you are not His. Heed His voice when you hear it. No matter how surprising a place or person from which it may come. If it is His voice, then you have heard Him.