This verse has proven problematic in the past. On the surface, it would appear that Alma is suggesting that the first resurrection consists of the rising of all people who lived and died from the days of Adam to the meridian of time- righteous and wicked alike- at the time of Christ’s resurrection.
We know from Abinadi (see Mosiah 15:21-22) and from modern revelation (see D&C 76:50-80) that only the celestial and the terrestrial bodies come forth in the first resurrection. Alma finally clarifies his meaning in verse 20 when he states that “the souls and the bodies are reunited, of the righteous, at the resurrection of Christ.” (See also Joseph Fielding Smith, Doctrines of Salvation 2:300; Answers to Gospel Questions 1:35-36.)