James L. Kugel and Rowan A. Greer, Early Biblical Interpretation, ed. Wayne A. Meeks (Philadelphia: Westminster, 1986) 139.
Barnabas 12 adds further complexities. [It] concludes by identifying Jesus as the true Joshua and the "Lord" of Psalm 110:1 and Isaiah 45:1. The Isaiah passage has been altered to read, "The Lord said to the Lord (Kyrio) my Christ" instead of "The Lord said to Cyrus (Kyro) my Christ." This altered verse occurs elsewhere in our sources. Could it be that the consonants are immutable jots and tittles, while the vowels can be changed, just as the rabbis felt able to alter the vocalization of the Hebrew text for purposes of interpretation, provided the consonants were preserved?
Greer cites three sources that apply Isaiah 45:1 to Jesus Christ rather than Cyrus: Barnabas 12:11, Novatian's On the Trinity 26, and Cyprian's Testimonies 1:21.
Barnabas (first-second centuries C.E.) uses Isaiah 45:1 to support his point about Psalm 110:1: that Jesus is Lord, not just the son of David.
Novatian (third century C.E.) uses Isaiah 45:1 to refute Sabellianism, which said that God was one person who performed three different roles: Father, Son, and Holy Spirit. Novatian said Isaiah 45:1 demonstrates that the Father and the Son are two separate persons, since the Father speaks to Christ, the Lord.
And Cyprian (third century C.E.) uses Isaiah 45:1 to demonstrate that Jesus Christ would rule the Gentiles, inviting them into a relationship with God.
I wonder if these three Christian interpreters thought about Isaiah 45:4-5 when they were applying Isaiah 45:1 to Christ. vv 4-5 explicitly state that the Messiah God is using to restore Israel does not know God. I'm sure that Barnabas, Novatian, and Cyprian would agree that Jesus knows God. So how can they apply Isaiah 45:1 to Jesus?
There was atomistic interpretation in ancient Judaism and Christianity, approaches that considered the Scriptures apart from their immediate contexts. Plus, Cyprian says that the Jews do not understand their Scriptures and that they must believe in Christ in order to do so (Testimonies 1:4-5). Paul says something similar in II Corinthians 3. This tells me that Christian interpreters believed one could read the Old Testament and not see Christ there, but that one needed Christian faith to look deeper into the text. I'm not sure what they would do with Isaiah 45:4-5. Would they say that, on the surface, the chapter appears to describe Cyrus, but it's really about Jesus?
The New Testament has the same sort of issue. John 13:18 applies Psalm 41:9 to Jesus' betrayal by Judas: "The one who ate my bread has lifted his heel against me" (NRSV). Yet, Psalm 41:4 presents the Psalmist saying "I have sinned against you." But Jesus didn't sin, so how can Psalm 41 apply to Jesus?
At the moment, I don't have a lot of scholarly evangelical works at my disposal. It may behoove me to read The Right Doctrine from the Wrong Texts?, which discusses the use of the Hebrew Bible in the New Testament. Here, I'll just check Jimmy Swaggart, John MacArthur, and John Gill to see how they handle John 13's application of Psalm 41:9 to Christ.
1. First of all, Jimmy Swaggart. In his Expositor's Study Bible, Swaggart sees more than one layer of meaning in Psalm 41. V 9, the passage that John 13:18 applies to Jesus, originally related to Ahithophel's betrayal of David during the revolt of Absalom, according to Swaggart. V 4, where the Psalmist says he has sinned, relates to (1.) David realizing that Absalom's revolt is God punishing him (David) for his sin with Bathsheba, (2.) God allowing the Antichrist to afflict the Jewish people on account of their rejection of Christ, and (3.) "Christ's interceding for Israel, making her rebellion his own." For Swaggart, (3.) would allow Christ to say he has sinned, even though he hasn't.
2. Second, John MacArthur. In the MacArthur Study Bible, MacArthur doesn't deal with the question of whether applying Psalm 41 to Christ makes Christ a sinner because of v 4. He assumes that the speaker of v 4 was a sinner, resulting in his sickness. In his treatment of v 9, MacArthur simply states: "David’s close companion betrayed him; he kicked him while he was 'down.' The Greater David’s experience and the employment of this reference in John 13:18 was to Judas (cf. Matt. 26:21ff.)." So MacArthur applies Psalm 41 to David, while he relates parts of it to the "greater David," Jesus Christ.
3. John Gill's treatment of Psalm 41:4 is interesting. He applies all of Psalm 41 to Christ, and that includes v 4:
for I have sinned against thee; or "unto thee", or "before thee", as the Targum; not that any sin was committed by him in his own person, but he having all the sins of his people on him, which he calls his own, Psa. 40:12; he was treated as a sinner, and as guilty before God, Isa. 53:12; and so the words may be read, "for I am a sinner unto thee" (u); I am counted as one by thee, having the sins of my people imputed to me; and am bound unto thee, or under obligation to bear the punishment of sin; or thus, "for I have made an offering for sin unto thee" (w), so the word is used, Lev. 6:26; and so it might be rendered in Lev. 5:7; and perhaps may be better rendered so in Lev. 4:3; and be understood, not of the sin of the anointed priest, but of his offering a sacrifice for the soul that sinned through ignorance, Psa. 41:2, which offering is directed to: and then the sense here is, heal me, acquit me, discharge me, and deliver me out of this poor and low estate in which I am; for I have made my soul an offering for sin, and thereby have made atonement for all the sins of my people laid upon me; and accordingly he was acquitted and justified, 1Ti. 3:16.
Gill offers two possible interpretations of Psalm 41:4: (1.) Like Swaggart, he says that Jesus called himself a "sinner" in the Psalm because he was taking on himself the sins of his people, meaning he was treated like a sinner when he was punished for their sins; (2.) Psalm 41:4 means, not that Jesus sinned, but that he offered a sin offering on behalf of sinners, the offering being himself.
Psalm 41:4 has the Hebrew chatati, "I sinned." Gill says that Leviticus 6:26 uses the same verb for "to offer a sin offering." I'm not sure if his reasoning works here, though, since Psalm 41:4 uses the qal, whereas Leviticus 6:26 has the piel.
One student told me that the Old Testament doesn't point to Christ in terms of a one-to-one correspondence, so we shouldn't expect full consistency between the verses in the Old Testament that supposedly foreshadow Christ, and the person of Christ. So why should we assume there's a connection in the first place? I wouldn't expect a non-Christian to believe that there is one. But, as a Christian, would there be a way for me to treat the Hebrew Bible with respect, while also allowing it to foreshadow Jesus Christ? Perhaps Christ or his followers saw in Jesus' experiences a reflection of what the Old Testament characters went through. In terms of Isaiah 45:1, maybe Christian exegetes had in mind what they saw as God's bigger plan, so they interpreted all of the Hebrew Bible in light of that, even if it wasn't always a fit.