The words of this speech by Alma are sufficiently beautiful that they have been set to inspirational music. The context is the meeting between Alma and the sons of Mosiah (confirmed in verses 14-17 below). This speech appears to be Alma’s response to Ammon’s joyful testimony recorded in Alma 26. It is important for the context of this sermon that we remember the events of the meeting of the sons of Mosiah and Alma:
Alma 27:16-19
16 And it came to pass that as Ammon was going forth into the land, that he and his brethren met Alma, over in the place of which has been spoken; and behold, this was a joyful meeting.
17 Now the joy of Ammon was so great even that he was full; yea, he was swallowed up in the joy of his God, even to the exhausting of his strength; and he fell again to the earth.
18 Now was not this exceeding joy? Behold, this is joy which none receiveth save it be the truly penitent and humble seeker of happiness.
19 Now the joy of Alma in meeting his brethren was truly great, and also the joy of Aaron, of Omner, and Himni; but behold their joy was not that to exceed their strength.
When Mormon recounts these events he does not specifically mention this speech by Alma, but the conditions will be seen to have sufficient parallels to this discourse that we may, with some assurance, assign this speech to that time.
Textual: This is an inserted soliloquy by Alma. Since the rest of the material appears to come from Ammon’s records, the placing of this speech and the locator indicates a change in source material. It is much more likely that Alma found this discourse in Alma’s record than that it would have been found with Ammon’s. It is clearly related to this occasion of the meeting of the old friends, but the sources and speakers are different. Mormon inserts the speech here with no introduction whatsoever. He has concluded the basic story of the mission of the sons of Mosiah, and has given his typical historical introduction. Then we get this speech with no introduction.
Most of the time we have seen Mormon create a new chapter when he switches sources, or inserts a speech from a different speaker. Here we learn that these guidelines that we can deduce were not hard rules. The content of Alma’s soliloquy clearly belongs with the story of the sons of Mosiah, and so he includes it here. Nevertheless, we may still presume that it is a different source from the abrupt addition. While there is no real proof of they hypothesis, it is almost as though he finished with the account of the sons of Mosiah, and when he returned to Alma’s sources, found this beautiful sermon, and decided to include it.