This is a very interesting and intriguing chapter with several lessons to teach us. It starts off fairly conventionally (at least in God's terms!). God send His word to a prophet to go and confront Jeroboam with his sin, and foretells the coming of King Josiah. It was some 300 years before this was fulfilled. He also gave a sign that this word was true. Jereboam rebels but is then struck with leprosy and the altar is duly split in two. Jereboam then becomes somewhat more contrite. The prophet prays for him and he is healed.
So far so normal.
Jereboam then wants to make friends with the prophet. However, God had told him not to return the same way home, and not to eat or drink, so he refuses.
So far so good, but on the way home an old, and somewhat corrupt, prophet meets him. This old prophet then tries to get the young one to come home with him, claiming that God had told him to say this. The young prophet now agrees to this. The word of the Lord then genuinely came to the old prophet and God pronounced judgement upon the young prophet who was duly killed by a lion. The old prophet seemed to have had some sort of respect for the young prophet and took care of the body and wanted to be buried with him when he died.
So what are we to make of all this. First there is Jeroboam, and here things are straight forward. He has sinned against God, he receives a word of judgement but did not repent, so he, and the nation, would suffer judgement. Note that Jereboam received his position as part of a prophecy, and was part of God's means of bringing judgement upon Solomon. This does not mean that he was not responsible for his own actions.
Now, let's turn to the young prophet. Some might think it a little unfair that he is so harshly judged for being deceived by this older prophet, but there is a valuable lesson for us here. All of us are responsible for our own actions, and our own response to God's word. The young prophet had received clear instructions from God, he disobeyed them.
Moreover, no matter who might give you a "word" or a "prophecy", the action you choose to take or not take is entirely your responsibility. I cannot say "I only did this because so and so said they believed it was God's will". My actions are my responsibility.
Note also how the young prophet passed the "big test" (rebuking to the king), but failed the "little test". We can easily be deceived.