Of all the passages of Scripture one seems to be most alarming to Christians, for I receive more questions about Hebrews 6:4-6 than about any other portion, especially when teaching concerning biblical admonitions and warnings.
Hebrews 6:4-6 does not only pose theological difficulty for English Christian readers but it also poses knotty exegetical difficulties for scholars. Thus, I confidently suggest that this entry and the next two (if so limited) will be the most head-ache inducing blog comments that I will have made to this blog to date.
This entry will be the first of at least three on this complex and difficult passage from the New Testament. This first entry will simply provide documentation of what others are saying concerning the passage. My own comments on the passage will follow in at least two subsequent entries in which I will first offer my own interaction with the scholars whom this entry cites followed by my own comments on the passage.
Consider the Greek text of Hebrews 6:4-6. If you desire to analyze the passage more closely for yourself with parsing aids, etc. click here. Below I provide the text with five key participles underlined. It is the fifth of these participles, παραπεσόντας ("fall away"), over which both theological and exegetical disputes continue.
Hebrews 6:4-6
ἀδύνατον γὰρ τοὺς ἅπαξ φωτισθέντας γευσαμένους τε τῆς δωρεᾶς τῆς ἐπουρανίου καὶ μετόχους γενηθέντας πνεύματος ἁγίου καὶ καλὸν γευσαμένους θεοῦ ῥῆμα δυνάμεις τε μέλλοντος αἰῶνος καὶ παραπεσόντας πάλιν ἀνακαινίζειν εἰς μετάνοιαν ἀνασταυροῦντας ἑαυτοῖς τὸν υἱὸν τοῦ θεοῦ καὶ παραδειγματίζοντας
In 1981 John Sproule, one of my professors during my MDiv and ThM days and the second reader of my ThM thesis, published a brief essay (six pages) on Hebrews 6:6 in which he argues that the five participles in Hebrews 6:4-6 should all be regarded as parallel and adjectival, and therefore the participle translated "fall away" should not be taken as conditional, which would be adverbial, but should be taken as a further, if final, characterizing of the same individuals who are described by the other four participles, all treated as adjectival. Thus, the preacher characterizes a group of people whom he presents as "those who were enlightened, who tasted, who were made partakers, who tasted, and who fell away" (John A. Sproule, “παραπεσόντα" in Hebrews 6:6,” Grace Theological Journal 2 [1981]: 327–332).
Sproule reasons,
The five participles in the series are accusative, plural, masculine participles and they all function as direct objects of the infinitive ἀνακαινίζειν (v 6 ). All five participles are introduced by the single article τούς and they are connected to each other by a simple connective series, τε . . . καὶ . . . καὶ . . . καὶ . . . καὶ. The
series is broken after παραπεσόντας. Thus the two remaining participles in the pericope (ἀνασταυροῦντας and παραδειγματίζοντας) are not part of the series and they are rightly construed as adverbial participles expressing cause. . . .
Further, a single article governing several adjectival participles in a series is also a legitimate Greek construction (cf. Gal 2:20, Rev 1:5). Since παραπεσόντας is governed by τοὺς and is part of the series of connected substantival participles, it cannot be adverbial so as to function conditionally. Thus, in the opinion of this writer, τοὺς . . . καὶ παραπεσόντας is best translated as a relative clause, “. . . and who have fallen away.”
John Sproule provides the following sentence diagram that fits his analysis of the passage (Sproule, “παραπεσόντα" in Hebrews 6:6,” GTJ 2 [1981]: 329).

To view the above chart more clearly click on the diagrammatical analysis chart to isolate the view upon the chart alone.
Others have latched on to Sproule's argument and have accepted it without offering their own exegesis. Consider four scholars in particular who cite Sproule's work as difinitive.
First, is R. Bruce Compton, "Persevering and Falling Away: A Reexamination of Hebrews 6:4-6" Detroit Baptist Seminary Journal (1996): 135-167.
The expression “fall away” is the fifth in a series of five parallel participles which begin in v. 4. These five participles are joined by simple conjunctions and are preceded by a single article. While an adverbial participle can introduce the protasis of a conditional clause, such does not appear to be the case here. The first four of these five participles are invariably taken with the article as adjectival and, specifically, as substantives in a series of relative clauses (“those who have once been enlightened and have tasted . . .”). Because all five appear to be parallel, there is every indication that the fifth should also be taken with the article as an adjectival substantive, continuing the series of relative clauses (“and have fallen away”). As such, it would not be adverbial and, hence, not conditional (pp. 141-142).
Second is Randall C. Gleason, "The Old Testament Background of the Warning in Hebrews 6:4-8," Bibliotheca Sacra 155 (1998): 71. Gleason reasons,
[T]he King James Version translation, “If they shall fall away” (v. 6), is unlikely because it is doubtful that the aorist participle παραπεσόντας, because of its linkage by a single article (τοὺς) to the preceding participles (vv. 4–5), was intended to express a condition. Neither does verse 6 have the conditional particle ἄν, which was usually used to introduce a conditional statement in Greek.
Third, Daniel Wallace (Greek Grammar Beyond the Basis: An Exegetical Syntax of the New Testament [Grand Rapids: Zondervan, 1996], 633) appeals to Sproule's essay when he comments that in Hebrews 6:6 it is debatable or doubtful that παραπεσόντας is a conditional participle. He argues,
Heb 6:4–6 ἀδύνατον τοὺς ἅπαξ φωτισθέντας (6) καὶ παραπεσόντας, πάλιν ἀνακαινίζειν εἰς μετάνοιαν
it is impossible to restore again to repentance those who have once been enlightened (6) if they have fallen away
παραπεσόντας is often construed as conditional (a tradition found in the KJV and repeated in most modern translations and by many commentators). But this is unwarranted. The construction of vv 4–6 approximates a Granville Sharp plural construction (the only difference being that with the second participle in the construction, γευσαμένους in v 4, the conjunction τε is used instead of καὶ: τοὺς φωτισθέντας γευσαμένους τε καὶ μετόχους γενηθέντας καὶ γευσαμένους καὶ παραπεσόντας). If this participle should be taken adverbially, then should we not take the preceding two or three participles the same way? The inconsistency has little basis. Instead, παραπεσόντας should be taken as adjectival, thus making a further and essential qualification of the entire group. A better translation, then, is “It is impossible to restore again to repentance those who have once been enlightened . . . and have fallen away.”
Fourth is Buist M. Fanning, "A Classical Reformed View," Four Views on the Warning Passages in Hebrews, ed. by Herbert W. Bateman IV (Grand Rapids: Kregel, 2007), 180, n. 16. Fanning appeals to John Sproule's brief essay and claims in a footnote,
The fifth participle is taken separately here for thematic reasons, but it is an integral, if final and surprsing, part of the grammatical construction in verses 4-6a (five participles governed by the single article τοὺς and joined by conjunctions τε or καὶ). It is not syntactically legitimate to take it as conditional ("if they fall away"), despite the major translations that render it this way (RSV, NIV).
It is evident that John Sproule's brief essay persuades the above four scholars to understand the sequence of five participles in Hebrews 6:4-6 as properly translated, in an expanded manner, as follows.
For it is impossible to renew unto repentance those who were once enlighted, who also once tasted the heavenly gift and who once were made partakers of the Holy Spirit and who once tasted the good word of God and the powers of the coming age and who once fell away because they are recrucifying the Son of God for themselves and subjecting him to open shame.
In other words, if the plural article (τοὺς) functions to render all five main participles adjectival ("those who" [substantival]), including the fifth (παραπεσόντας), then the adverb (ἅπαξ), meaning "once" (in the numeric sense, "once but not now") or "once for all" (in the conclusive sense), must also be distributed to the four subsequent participles. Thus, τοὺς ἅπαξ not only attaches conceptually to the first four participles but also to the fifth. So, "those who were once enlighted" are being described as "those who once tasted the heavenly gift" and "those who once were made partakers of the Holy Spirit" and "those who once tasted the good word of God and the powers of the coming age" but also "those who once fell away."
If these gentlemen are correct, this has no small ramifications for how we are to understand Hebrews 6:4-6.