There are three New Testament passages that I'd like for us to consider:
"Let every soul be subject to the governing authorities. For there is no authority except from God, and the authorities that exist are appointed by God. Therefore whoever resists the authority resists the ordinance of God, and those who resist will bring judgment on themselves. For rulers are not a terror to good works, but to evil. Do you want to be unafraid of the authority? Do what is good, and you will have praise from the same. For he is God's minister to you for good. But if you do evil, be afraid; for he does not bear the sword in vain; for he is God's minister, an avenger to execute wrath on him who practices evil. Therefore you must be subject, not only because of wrath but also for conscience' sake."
Although these passages are not as explicit as some of the Old Testament verses, they do authorize the death penalty today as a function of civil government. Allow me to elaborate. The apostles Peter and Paul commanded obedience to governing authorities (and they issued that command while living under a corrupt Roman government). We today, whether we like it or not, must obey our government's laws (except any legislation that attempts to force us to act in a sinful way; e.g., Acts 4:19; 5:29).
Whether we understand it or not, God appoints the civil governments that exist. According to God, the fundamental role of government is to praise those who do good and execute wrath on evildoers. That's what God has authorized and empowered his minister--civil government--to do! Paul goes on to explain that civil government "does not bear the sword in vain". This undeniably opens the door to capital punishment today, for the sword, among other things, is a tool suitable for taking life. Paul understood this and acknowledged (before Festus) the right of the government to execute those who commit crimes deserving of death. Civil authorities (which are separate from religious authorities under the New Testament) are to use their "sword" as "an avenger to execute wrath on him who practices evil." God has authorized civil authorities today to punish evildoers, even to the taking of life.
Although personal, individual vengeance has never been authorized under any dispensation, God has authorized a certain avenger in both covenants. We will explore the topic of vengeance in our final lesson in this series and also deal with some objections to the use of the death penalty today.