This is the constant problem. People do not care about religion. So when someone like Nephi delivers a message to the audience that is threatening because it contradicts their presumptions, they get upset. They are fearful. They "tremble, and are angry." When Nephi puts out the message, he knows those he addresses are going to react in a very negative way. He will become the object of their distrust and dislike.
But Nephi reminds the audience that it isn't him they have a problem with. It is "the truth of God."
There are two reactions: One is anger, because it condemns them. The other is gladness. Those who are "built upon the rock" --meaning Christ-- have their hope and faith in Him, for He is the "Rock of Heaven,"(Moses 7: 53) and they "receive it with gladness."
Those who are "built upon a sandy foundation" will "tremble." This would mean they are struck with fear. They are afraid of the message. They fear because they begin to realize their religious convictions may be wrong. They are afraid they "shall fall," or in other words, if the message is true then they may be doomed and their high hopes dashed.
They would rather be angry and try and suppress the message than to receive it and repent. If someone has a good heart, then any warning is appreciated. Even if it informs them they are mistaken. They want truth. So a warning is appreciated when it permits them to correct their errors. These people are built upon the Rock, because truth alone determines what they will accept. They "hearken to the truth" because they are interested in knowing truth.
This message from Nephi reminds all of us about the difference between those who are grounded in the testimony of Jesus (the Rock) and those who hope their brand of religion will aid them (the sand). False hopes are quickly threatened when exposed to the truth. Knowledge that you are built upon the testimony of Jesus, however, cannot be shaken. Critics will be ground into dust by such a stone, but will not damage it. (Daniel 2: 45.) Those with such knowledge would suffer death, but not deny the Lord. (Mosiah 17: 10.) Though called upon to suffer for His name, they will not submit, but choose to die secure in the knowledge they have of Christ. (D&C 138: 13-14.)
This kind of faith requires sacrifice, as explained in the Lectures on Faith previously posted. The Book of Mormon calls it "knowledge" and that lecture requires you "actually know the course you are pursuing is pleasing to God." That is, whether you call it "faith" as the Lectures do, or "knowledge" as the Book of Mormon does, it is the same. You must come to know Christ has accepted your sacrifices. You should re-read that if you want to reacquaint yourself with the requirements for gaining such faith.