After the angel appeared to Alma to send him back to Ammonihah, he returned speedily (v. 18). Yet, Alma seems to take his time before preaching again. He deliberately spends many days with Amulek. This wasn't because Alma was lazy or afraid of the people. It was important for him to teach Amulek and his family so that Amulek could accompany him on his mission. Again, Alma shows a great understanding of the things of the Spirit. Once he arrives in Ammonihah, he does not make the mistake of rushing out to preach without first spending an adequate amount of time with his first convert and next missionary companion.
Henry B. Eyring
"…by the power of the gospel of Jesus Christ, Amulek was transformed from someone who resisted the word of God into a powerful preacher of righteousness. And it took only days, not months or years. The record says that Alma stayed in Amulek's home for 'many days' (Alma 8:27). During that time Alma taught Amulek. And an angel, perhaps the one who first commanded Amulek to receive Alma into his home, came to him to confirm what Alma taught. Amulek stated, 'And again, I know that the things whereof he hath testified are true; for behold I say unto you, that as the Lord liveth, even so has he sent his angel to make these things manifest unto me; and this he has done while this Alma hath dwelt at my house' (Alma 10:10).
"By obeying Christ's authority through His servants, Amulek was blessed with the power to lead others to eternal life in ways he could not have seen in advance. He was given immediately the gift to teach people to feel a compelling need to have all their sins washed away. As you listen to his voice in his first sermon, take hope that God could bless you and me with such a mighty change." (Heroes From the Book of Mormon, p. 107-8)