The Kingdom Consolidated

Now the sons of Rimmon the Be-er′othite, Rechab and Ba′anah, set out, and about the heat of the day they came to the house of Ish-bo′sheth, as he was taking his noonday rest. And behold, the doorkeeper of the house had been cleaning wheat, but she grew drowsy and slept; so Rechab and Ba′anah his brother slipped in. When they came into the house, as he lay on his bed in his bedchamber, they smote him, and slew him, and beheaded him. They took his head, and went by the way of the Arabah all night, and brought the head of Ish-bo′sheth to David at Hebron. And they said to the king, “Here is the head of Ish-bo′sheth, the son of Saul, your enemy, who sought your life; the Lord has avenged my lord the king this day on Saul and on his offspring.” But David answered Rechab and Ba′anah his brother, the sons of Rimmon the Be-er′othite, “As the Lord lives, who has redeemed my life out of every adversity, when one told me, ‘Behold, Saul is dead,’ and thought he was bringing good news, I seized him and slew him at Ziklag, which was the reward I gave him for his news. How much more, when wicked men have slain a righteous man in his own house upon his bed, shall I not now require his blood at your hand, and destroy you from the earth?”
— 2 Samuel 4:5-11

From this passage we see that David and Jesus Will Always Do things the right and righteous way, therefore we should never doubt his methods or plans, whatever is going on in the world. David punishes Ish-Bosheth’s murderers, just like the Amalekite, with Capital Punishment, and this displays God and Christ’s holiness and justice.

He who passively accepts evil is as much involved in it as he who helps to perpetrate it. He who accepts evil without protesting against it is really cooperating with it
— Martin Luther King, Jr.

This biblical concept of complicity is very evident in this chapter, which is why David must absolve himself in justice and why God must execute the justice which His holiness requires. 

Though the wicked is shown favor, He does not learn righteousness; He deals unjustly in the land of uprightness, And does not perceive the majesty of the LORD.
— Isaiah 26:10

Some people seem simply incorrigible, they seem hell-bent on evil to the point where they are asking to be killed rather than reform, and capital punishment is actually a mercy to these types of people, before they rack up more guilt in the eyes of God before going to hell, thus making their punishment there worse.

Should we pray for repentance and reform? Absolutely. But we must never believe that we as men, or any society, or prison, or man-made rehabilitation can actually change someone's heart. God alone can, and for that we should pray. But David shows his own righteousness and lack of complicity with the murders in punishing the evil-doers he is now king over.

Jesus also will bring a sword with him when he returns, for in the second coming it will be a time of both mercy and justice (unlike his first coming where he said he came not to judge). The righteous and the wicked alike should be reminded that that day is coming.

Let the evildoer still do evil, and the filthy still be filthy, and the righteous still do right, and the holy still be holy.
— Revelation 22:11

In Prayer Today: 

Seek the Lord while He may be found, that you may come in under His mercy, not His justice.