Alma having knowledge of the people believing his words (v. 17) is a gift of the Spirit that is not often mentioned. Just as Nephi testified, “when a man speaketh by the power of the Holy Ghost, the power of the Holy Ghost carrieth it unto the hearts of the children of men” (2 Nephi 33:1), so will the Spirit carry the message back to the speaker that his hearers know the truthfulness of the message. The joy Alma experienced will accompany that message when the news is good. In this case, Alma’s desires and perceptions had been met (Alma 7:18–19).
The path to eternal life that leads to the kingdom of God is the path of Jesus Christ that we must follow (see 2 Nephi 31:9–10). Since he does not walk in crooked paths nor vary from turning to the right or to the left (v. 20), neither can we. Nephi, son of Lehi taught the same doctrine. He testified that “he is the same yesterday, today, and forever … wherefore, the course of the Lord is one eternal round” (1 Nephi 10:18–19). Alma later gives the same counsel to his son Helaman (see Alma 37:12). The Lord confirmed this doctrine to the Prophet Joseph Smith relating to the loss of the 116 pages of manuscript.
1 The works, and the designs, and the purposes of God cannot be frustrated, neither can they come to naught.
2 For God doth not walk in crooked paths, neither doth he turn to the right hand nor to the left, neither doth he vary from that which he hath said, therefore his paths are straight, and his course is one eternal round. [D&C 3:1–2]
The accompanying doctrine of the Lord not dwelling in unholy temples (Alma 7:21) goes hand in hand with his unvarying course. That Christ does not dwell in unholy temples was also taught by Paul.
16 Know ye not that ye are the temple of God, and that the Spirit of God dwelleth in you?
17 If any man defile the temple of God, him shall God destroy; for the temple of God is holy, which temple ye are. [1 Corinthians 3:16–17]
The light of Christ is given to every person born into the world (see John 1:9; Moroni 7:16; see also D&C 84:46). “And every man whose spirit receiveth not the light is under condemnation” (D&C 93:31). Likewise, the Holy Ghost “may descend upon [a person] and not tarry with him” (D&C 130:23). For this reason Paul admonished the Corinthian saints to flee fornication because it was a sin “against [their] own body” and their “body [was] the temple of the Holy Ghost which is in you” (1 Corinthians 6:18–19). Those who drive out the Holy Ghost and the light of Christ will, in the last day, be filthy and “he who is filthy shall remain in his filthiness” (Alma 7:21) and cannot dwell in the kingdom of God (see 1 Nephi 15:33).