Summary: Godliness exalts a nation. Ungodliness condemns a nation. A study of the migration of godly people from a nation turning from righteousness and the impact their leaving had on that nation and the nation to which the immigrated.
“The priests and the Levites who were in all Israel presented themselves to him from all places where they lived. For the Levites left their common lands and their holdings and came to Judah and Jerusalem, because Jeroboam and his sons cast them out from serving as priests of the LORD, and he appointed his own priests for the high places and for the goat idols and for the calves that he had made. And those who had set their hearts to seek the LORD God of Israel came after them from all the tribes of Israel to Jerusalem to sacrifice to the LORD, the God of their fathers. They strengthened the kingdom of Judah, and for three years they made Rehoboam the son of Solomon secure, for they walked for three years in the way of David and Solomon.” 
Spiritual leaders from the Northern Kingdom, together with many individuals who wanted to honour the Living God, migrated to the Southern Kingdom. There, their presence “strengthened the kingdom of Judah.” I find it fascinating to note that the Word of God states that their exodus from Israel made Rehoboam “secure.” Migration from the northern kingdom made the southern kingdom secure. I suppose it would have been easy to complain that it was a gentle revolution and that such an influx would threaten the culture. However, the Bible saw matters differently. It is essential that we recognise that this was not an invasion that would alter the culture of Judah; those moving into the kingdom would adopt the culture of their new nation rather than insisting that Judah adapt to them.
You may recall that Jeroboam had compromised the Faith and led the people into gross idolatry. It wasn’t that he meant to dishonour God, but he couldn’t trust God to secure his kingdom, so he took matters into his own hands and made representations of the God of Heaven so that people wouldn’t seek God in His Temple in Jerusalem. The result was that Jeroboam so compromised the Faith that people of conscience could not tolerate what Israel had become.
However, let’s go back to the beginning. God promoted Jeroboam to reign over the northern tribes, tearing those tribes from Solomon’s son because of compromise, Jeroboam was not willing to trust God to keep him on the throne. The Word pointedly states that God exalted this man Jeroboam, elevating him to the throne of what would become the northern kingdom. We read the account in the First Book of the Kings. “Jeroboam the son of Nebat, an Ephraimite of Zeredah, a servant of Solomon, whose mother’s name was Zeruah, a widow, also lifted up his hand against the king. And this was the reason why he lifted up his hand against the king. Solomon built the Millo, and closed up the breach of the city of David his father. The man Jeroboam was very able, and when Solomon saw that the young man was industrious he gave him charge over all the forced labor of the house of Joseph. And at that time, when Jeroboam went out of Jerusalem, the prophet Ahijah the Shilonite found him on the road. Now Ahijah had dressed himself in a new garment, and the two of them were alone in the open country. Then Ahijah laid hold of the new garment that was on him, and tore it into twelve pieces. And he said to Jeroboam, ‘Take for yourself ten pieces, for thus says the LORD, the God of Israel, “Behold, I am about to tear the kingdom from the hand of Solomon and will give you ten tribes (but he shall have one tribe, for the sake of my servant David and for the sake of Jerusalem, the city that I have chosen out of all the tribes of Israel)”’” [1 KINGS 11:26-32].
Think this through; God chose Jeroboam and promoted him to a position of authority. God did this because of the sin of Solomon. In this same passage, we see God saying of Solomon and of what would become the land of Israel, “[Solomon has] forsaken me and worshiped Ashtoreth the goddess of the Sidonians, Chemosh the god of Moab, and Milcom the god of the Ammonites, and they have not walked in my ways, doing what is right in my sight and keeping my statutes and my rules, as David his father did. Nevertheless, I will not take the whole kingdom out of his hand, but I will make him ruler all the days of his life, for the sake of David my servant whom I chose, who kept my commandments and my statutes. But I will take the kingdom out of his son’s hand and will give it to you, ten tribes. Yet to his son I will give one tribe, that David my servant may always have a lamp before me in Jerusalem, the city where I have chosen to put my name. And I will take you, and you shall reign over all that your soul desires, and you shall be king over Israel. And if you will listen to all that I command you, and will walk in my ways, and do what is right in my eyes by keeping my statutes and my commandments, as David my servant did, I will be with you and will build you a sure house, as I built for David, and I will give Israel to you” [1 KINGS 11:33-38].