Even though Alma had already given counsel to his sons, he gives them a final blessing, as well as giving the earth a general blessing. The “blessing”, recorded in verse 16, is more of a curse. It is the declaration of the negative aspect of the covenant of the land. The land will be cursed for those who do wickedly. Perhaps some of that sentiment was based on the destruction of the war of the eighteenth year. Perhaps, even more, it was based upon his prophetic vision of the ultimate destruction of the Nephite people.
Mormon doesn’t record Alma’s blessing on the church, but it surely was not as gloomy as verse 16. Nevertheless, for Mormon’s purposes, it was the penalty of verse 16 that he was living through, and therefore that cursing would have been most poignant for him as he wrote.