Two verses that I have always been blessed by (and likewise been encouraged/exhorted by) are regarding two different kings of Judah:
King Hezekiah - 2 Kings 18:5-7a He trusted in the LORD God of Israel; so that after him was none like him among all the kings of Judah, nor any that were before him. For he clave to the LORD, and departed not from following him, but kept his commandments, which the LORD commanded Moses. And the LORD was with him; and he prospered whithersoever he went forth.
No king had ever trusted the Lord God quite like King Hezekiah did - he followed the Lord and clung to Him, turning to Him anytime he was faced with difficulties in his life and reign. He trusted the Lord to work all things out for him, and turned to Him in prayer first before resolving the situation that distressed him. A lesson for us all!
King Josiah - 2 Kings 23:25 And like unto him was there no king before him, that turned to the LORD with all his heart, and with all his soul, and with all his might, according to all the law of Moses; neither after him arose there any like him.
No other king turned to the Lord with all his heart quite like King Josiah did - with all his heart, soul, and might. Does that remind you of any New Testament verses that we are all commanded to follow? (See Matthew 22:27-38 and Mark 12:30.)
Between these two kings, we have a great example to follow - both in learning to trust the Lord more and in turning to Him with all our heart. God will bless His children that follow Him with a perfect (complete, full) heart:
2 Chronicles 16:9a For the eyes of the LORD run to and fro throughout the whole earth, to shew himself strong in the behalf of them whose heart is perfect toward him.
A third king to learn from is King Solomon - 1 Kings 3:12 Behold, I have done according to thy words: lo, I have given thee a wise and an understanding heart; so that there was none like thee before thee, neither after thee shall any arise like unto thee.
He petitioned the Lord for wisdom at the beginning of his reign - and God blessed him with wisdom so much that no one else in history (except for the Lord Jesus Christ Himself) could even compare. A good lesson to learn: that wisdom only comes from the Lord - and as much as you need is free for the asking! (See James 1:5.) Unfortunately, Solomon also made some really foolish choices later in life - the greatest one was his lack of separation in marrying heathen wives. These led him away from the Lord into abominable idolatries. I do believe he repented of these sins later in his life and wrote the book of Ecclesiastes as his testimony of how a life lived in fulfillment of fleshly gratification is "vanity of vanities." True fulfillment is only found in the Saviour and in His will for our lives. May we all learn that lesson!
With each good example, there are also bad examples. One of which is king Ahab, who married that horribly wicked woman, Jezebel:
King Ahab - 1 Kings 21:25-26 But there was none like unto Ahab, which did sell himself to work wickedness in the sight of the LORD, whom Jezebel his wife stirred up. And he did very abominably in following idols, according to all things as did the Amorites, whom the LORD cast out before the children of Israel.
But this wicked king later repented, and God had mercy upon him.
1 Kings 21:27-29 And it came to pass, when Ahab heard those words, that he rent his clothes, and put sackcloth upon his flesh, and fasted, and lay in sackcloth, and went softly. And the word of the LORD came to Elijah the Tishbite, saying, Seest thou how Ahab humbleth himself before me? because he humbleth himself before me, I will not bring the evil in his days: but in his son's days will I bring the evil upon his house.
Another king who did very wickedly during his long reign was Manasseh:
King Manasseh - 2 Chronicles 33:9 So Manasseh made Judah and the inhabitants of Jerusalem to err, and to do worse than the heathen, whom the LORD had destroyed before the children of Israel.
God warned this wicked king, and eventually brought judgment:
2 Chronicles 33:10-11 And the LORD spake to Manasseh, and to his people: but they would not hearken. Wherefore the LORD brought upon them the captains of the host of the king of Assyria, which took Manasseh among the thorns, and bound him with fetters, and carried him to Babylon.
BUT the Lord's judgment was tempered with mercy, and it humbled a rebellious sinner:
2 Chronicles 33:12-13 And when he was in affliction, he besought the LORD his God, and humbled himself greatly before the God of his fathers, And prayed unto him: and he was intreated of him, and heard his supplication, and brought him again to Jerusalem into his kingdom. Then Manasseh knew that the LORD he was God.
I can't read that passage without tears coming to my eyes. The same mercy offered to that rebellious, utterly wicked king has been offered to me - and that same mercy that saved that utterly wicked king saved this same wicked sinner. Notice what God's Word says about Manasseh and his genuine repentance:
...he besought the LORD his God...
...and humbled himself greatly before the God of his fathers...
...And prayed unto him, and he was intreated of him, and heard his supplication...
...Then Manasseh knew that the LORD he was God...
Manasseh repented (he changed his mind, resulting in a change in his conduct); this is obvious from the following verses:
2 Chronicles 33:14-16 Now after this he built a wall without the city of David, on the west side of Gihon, in the valley, even to the entering in at the fish gate, and compassed about Ophel, and raised it up a very great height, and put captains of war in all the fenced cities of Judah. And he took away the strange gods, and the idol out of the house of the LORD, and all the altars that he had built in the mount of the house of the LORD, and in Jerusalem, and cast them out of the city. And he repaired the altar of the LORD, and sacrificed thereon peace offerings and thank offerings, and commanded Judah to serve the LORD God of Israel.
Now Manasseh could not undo ALL his wickedness, but he certainly made a good attempt. The account of his life ends with the following words:
2 Chronicles 33:18-19 Now the rest of the acts of Manasseh, and his prayer unto his God, and the words of the seers that spake to him in the name of the LORD God of Israel, behold, they are written in the book of the kings of Israel. His prayer also, and how God was intreated of him, and all his sin, and his trespass, and the places wherein he built high places, and set up groves and graven images, before he was humbled: behold, they are written among the sayings of the seers.
Manasseh humbled himself and turned to the Lord God, in repentance and faith - he got saved and his life was changed eternally.
Definitely some lessons worth learning! But the greatest lesson of these kings (at least to me) - the King of Lessons - is that God has mercy enough and to spare for those who will humble themselves in repentance when they hear the Gospel of Christ, which is the power of God unto salvation, and turn to the Lord Jesus Christ in faith to save them from all their sins. The King of Kings offers mercy to all who will receive it - "whosoever will may come."