“For He made Him who knew no sin to be sin for us [huper hēmōn], that we might become the righteousness of God in Him” (emphasis mine). This statement is made in the context of verses 14-15, which says: “For the love of Christ compels us, because we judge thus: that if One died for all [huper pas], then all died; (15) and He died for all [huper pas], that those who live should live no longer for themselves, but for Him who died for them [huper autos] and rose again” (emphases mine). As you’ve noticed, huper is well represented in these verses. In his commentary on 2 Corinthians, at verse 14, Charles Hodge pointed out that huper “may have the general sense, for the benefit of, in behalf of, or the stricter sense, in the place of” (emphases in the original). He followed this with:
In all those passages in which one person is said to die for another … or in which the reference is to a sacrifice, the idea of substitution is clearly expressed. The argument does not rest on the force of the preposition, but on the nature of the case. The only way in which the death of the victim benefited the offerer, was by substitution. When, therefore, Christ is said to die as a sacrifice for us, the meaning is, he died in our stead. His death is taken in the place of ours so as to save us from death.
Now, there should be no doubt as to Hodge’s theological leanings, in that he embraced Reformed theology through and through. Therefore, what he said in the above quotes could be more a reflection of Reformed thinking (as Barnett and others will, no doubt, believe) than his linguistic skills and scholarship (as I tend to think). Either way, what he said is something which must be given a great deal of consideration by all who are honestly trying to think this subject through. And, even though it’s true we all have our “preunderstandings,” as our presuppositions are now being called, our particular brand of hermeneutics (viz., the grammatical-historical method) is designed to help us circumnavigate these preunderstandings as we attempt to correctly exegete Scripture. Thus, I long for the day when our discussions of these matters are able to break free of wranglings over the definitions of words apart from their context, as all such definitions are dubious as far as I can tell. Truth is, words, sentences, and thoughts are connected, and because they are, every effort must be made to learn how they relate and derive their meanings. In other words: Context! Context! Context!
With this in view, let’s take a look at 2 Corinthians 5:20, which reads, “Now then we are ambassadors for Christ [huper Christou], as though God did beseech you through us: we pray you in Christ’s stead [huper Christou], be ye reconciled to God” (KJV, emphases mine). Now, whether huper Christou is rendered “in Christ’s stead” as it is here in the KJV or “on Christ’s behalf” as in the NKJV, or simply “for Christ” as in the first entry above, the context indicates some sort of substitution or “in place of” action taking place. Paul was an ambassador “on behalf of” or “in the place of” Christ—i.e., in His stead. Therefore, it makes no difference which particular set of words are used here, in that the idea being conveyed is that Paul was doing something “in Christ’s stead” (KJV)—i.e., “as though God were pleading through [him for them to be] reconciled to God.” By the time we get to verse 21, then, the flow of things (i.e., the context) has to do with someone doing something in the place of or on behalf of another, whether it be what Christ did “for us” or “in our stead” (v. 14) or what Paul, acting in Christ’s stead, was doing for the saints. Thus, everything I know about hermeneutics tells me it is reasonable to believe that verse 21 is speaking of something Jesus did not just on our behalf, but in our stead as well.
Having said this, I want to make it clear that I recognize that an “on our behalf” definition of huper in verse 21 minus an “in place of” meaning, which is the default position of those who hold the non-substitutionary-death-of-Jesus position, is a possibility, in that “on behalf of” does not necessarily carry with it the idea of “in place of” or “instead of.” However, I do not see this as very likely, and this due to the context in which it exists. Further, it must not be forgotten that verse 21 exists not only in its specific and general context, but the even larger context of everything God has had to say about this; namely, “The entirety of Your word is truth, and every one of Your righteous judgments endures forever” (Psa. 119:160).
This is a truth I plan to expand upon in the posts that follow, particularly the final one. In the meantime, don’t let anyone fool you into thinking the Bible nowhere mentions the Lord’s substitutionary death. Truth is, the idea or concept contained within the meaning of hupe can, depending on the context, easily mean “in place of” or “instead of,” and I have every reason to believe that most—if not all—who’ve spent much time on this subject know it.
In the post that follows, I plan to focus on Galatians 3:13 and its context.
 Charles Hodge, An Exposition Of II Corinthians, PDF, 1997, p. 149, located at http://truth4freedom.files.wordpress.com/2012/11/hod_2cor.pdf.↩
 Concerning Paul’s ambassadorship, see Ephesians 6:20.↩