22 Now, one of them, whose brother had been slain with the sword of Ammon, being exceedingly angry with Ammon, drew his sword and went forth that he might let it fall upon Ammon, to slay him; and as he lifted the sword to smite him, behold, he fell dead.
23 Now we see that Ammon could not be slain, for the Lord had said unto Mosiah, his father: I will spare him, and it shall be unto him according to thy faith—therefore, Mosiah trusted him unto the Lord.
Let them go up, for many shall believe on their words, and they shall have eternal life; and I will deliver thy sons out of the hands of the Lamanites (Mosiah 28:7).
On the basis of that promise, Mosiah allowed his sons to go.
In the passage above, Mormon shares a dramatic experience in which the Lord kept his promise. As Ammon lay unconscious, an angry man attempted to kill him. The attacker immediately fell dead, with no apparent cause. Mormon takes the opportunity here to remind us of the promise God had made to King Mosiah in order to teach us an important principle: God always keeps His promises. We can trust Him.
Today, I will remember some of the promises God has made to me: in my patriarchal blessing, in the ordinances I have received, and in specific answers to my personal prayers. I will act in faith and will trust that He will keep His promises to me just as He kept His promise to Mosiah.