This verse simply states a fact: Abijah, the son of King Jeroboam, fell ill.

Here's what we can glean from this single verse in the larger context of the story:

Introduction to a Narrative: This verse serves as the opening line of a larger narrative. It immediately sets the stage for a story about Abijah's illness and what will follow.
Sets the Stage for Jeroboam's Actions: The sickness of Jeroboam's son acts as a catalyst for what Jeroboam does next. He's clearly concerned for his son and will take action because of this illness.
Highlights the Significance of Abijah: The fact that the Bible mentions the illness of a royal son suggests that Abijah might be a significant character in the story. It raises the question of whether he's just an ordinary boy or if his life has greater meaning or potential, especially in light of Jeroboam's reign.
Foreshadowing: Often in biblical narratives, illness, especially of a prominent figure, can foreshadow larger themes of judgment or redemption. While we can't be certain, it hints that something significant will come of this event.
Humanizes Jeroboam: Despite Jeroboam's generally negative portrayal in the Bible (due to his idolatry and leading Israel into sin), the verse implies a fatherly concern for his son. This humanizes him to some extent.

In essence, this verse is a simple statement that sets the stage for the drama to unfold, introducing a key character and hinting at the importance of the events to come. The following verses reveal that Jeroboam sends his wife in disguise to the prophet Ahijah to inquire about Abijah's fate.