What is the Biblical basis for the "penal" in penal substitutionary atonement? I have been looking at different models of the atonement and am currently looking at penal substitutionary atonement.  While I can see the substitution, I'm struggling somewhat with the idea of Jesus taking the penalty for our sin.

So, what is the Biblical basis for the "penal" in penal substitutionary atonement?
The 'penal' in penal substitution is based on the idea that sin brings about punishment under the curse of the law.  The curse of Adam's sin is death, which is a punishment. Punishment = the curse under the law for sin.


  Christ redeemed us from the curse of the law by becoming a curse for us, for it is written: “Cursed is everyone who is hung on a pole.” (NIV Galatians 3:13)


For Christ to become a curse is the same thing as saying he became guilty for our sin, or more emphatically became our actual sin making the Law execute him under its wrath:


  God made him who had no sin to be sin for us, so that in him we might become the righteousness of God. (NIV 2 Corinthians 5:21)


To say the holy Son of God is 'sin' and is 'cursed' must presume at the same time that he deserves to be punished for us, otherwise these appellations have no actual meaning and are blasphemy.  

What you will find in reviewing different theories of atonement is that there are actually only two. These theories either support what is called a forensic justification by faith, or a denial of such a thing. The penal theory is actually just a natural result of affirming the reformed doctrine of Justification by faith. Anyone else when using the term 'justification' merely mean an initial point of sanctification. They mean some sanctification is necessary involved in producing justification. Justification to them means more of an initial 'full sanctification' making a person personally and inwardly righteous. The reformers just call this justification by works under the gloss of fake grace. Just legal righteous to serve the self righteous desires of those who deny the full curse of original sin. 

The reformers denied any kind of inner righteousness having any involvement in justification in any sense.  Therefore while the penal theory supports a means whereby an absolutely evil person can be declared righteous apart from any work whatsoever, non penal theories focus on some infused righteousness as a result of Christ's death and our faith in him. The result is they avoid the penal aspect clearly spelled out by Paul and look for other subjects such as moral improvements, fatherly relationships, mystical unions, spiritual redemption....or any other focus that would allow some righteous ability of a person to cooperate with the Spirit and somehow retain some kind of human goodness. In other words the penal concept come from both the doctrines of original sin and justification apart from works.

Historically the penal idea is simply the acceptance of Pauline legal arguments as a necessary result of abandoning humanity to an absolutely hopeless sate under original sin. When man is absolutely lost and no method to relieve his 'guilt' or deserved 'punishment' under the Law, someone must pay before any sanctification can occur. This order of Justification before any sanctification, is the 'forensic' or 'external legal' doctrine of justification. 

What I am trying to say is that although scriptures that I have quoted explain the origin of the penal theory it is actually the entire New Testament doctrine of original sin, the Incarnation, the death of Chris itself and all of the Epistles, especially that of Paul's 'legal arguments' around justification that forced the penal theory out of the reformation.

Basically is is Paul the Apostle who insisted on it at first. By keeping justification 'apart from works', 'justification' must necessarily come before sanctification. Sanctification must be the immediate but separate result of being externally justified apart from previous or combined inner just qualities. Once justification has at least conceptualy been separated from sanctification there can be no moral improvement in the sinner involved in atonement (accept as the resulting reconciliation of the sinner). Therefore, to get rid of sin someone else has to take it as their own along with any curse and punishment sin deserves. So you see it's doctrinal. If justification comes first apart from works (sanctification) then to deny a penal substitution is simply to deny that sin should ever be punished.

In other words:


  For what the law was powerless to do because it was weakened by the flesh, God did by sending his own Son in the likeness of sinful flesh to be a sin offering. And so he condemned sin in the flesh, in order that the righteous requirement of the law might be fully met in us, who do not live according to the flesh but according to the Spirit. (NIV, Romans 8:3-4)


To a reformer of course God the Father punished / condemned sin in Christ as a sin offering for us. This with us initially and inwardly 'outside of the legal transaction', other than of course our own guilt and sin being legally transferred to Christ, in order to make him guilty for us and punished for us.

So if Christ is to be made sin, made a curse, to be condemned in the flesh for our sin, what idea could ever possibly arise that would make one attempt to avoid the 'penal' implications!?