But the penalty and act of carrying out the punishment for sin changed dramatically between the New and Old.
One is a theocracy ... (OT .. time from Moses to end of OT text)
One is not -- (All of the NT)
A theocracy is a government where God is King and the Laws are His, Sin is rebellion against the King and gross sin is treason. In a theocracy God protects the nation and defeats its enemies - and dictates its rules.
But outside the theocracy it is a different story. Not only is God not taking the helm but Christians are slandered, persecuted, martyred and God is not dictating the death penalty for blasphemy or Sabbath breaking or worship of false gods or coveting etc.
The Gospel however brings up the point that for the sin of coveting - one dies - in fact... the lake of fire.
Romans 6:23 - "For the wages of sin [is] death; but the gift of God [is] eternal life through Jesus Christ our Lord."
the punishment for sin, is not receiving eternal life in the kingdom of heaven, not to be murdered by man.
On the contrary - the punishment in Rom 6:23 is the second death mentioned in Rev 20 - roasted alive in fire and brimstone - lake of fire. And that means any sin -- including thought crimes like "coveting" see Romans 7.
All the wicked in both OT and NT (many billions) - are resurrected in Rev 20 and roasted alive in the lake of fire. Far more will be slain in executive judgment (many billions) in the NT than in all of the OT combined.
Jesus said in John 11 - (after Lazarus suffered a slow painful death of sickness ) that this does not even count at all. That the second death is so much worse that Lazarus's death is not considered real death in God's eyes.
In the lake of fire "both body and soul" are destroyed in fire and brimstone Matt 10:28 -- but each person suffers in proportion to their evil deeds.
Luke 12:47 And that slave who knew his master’s will and did not get ready or act in accordance with his will,
will receive many blows, 48 but the one who did not know
it, and committed acts deserving of a beating,
will receive only a few blows. From everyone who has been given much, much will be demanded; and to whom they entrusted much, of him they will ask all the more.