In Hebrews 6:4–5, to have been “enlightened” means to have experienced conversion (Heb. 10:32). It refers to those who have turned from the “darkness” of the power of Satan to the “light” of God (Acts 26:17, 18). It implies deliverance from sin (Eph. 5:11) and ignorance (1 Thess. 5:4, 5). The verbal form here suggests that this enlightening is an act of God achieved through Jesus, “the brightness of His glory” (Heb. 1:3, NKJV).

To “have tasted the heavenly gift” and to “have become partakers of the Holy Spirit” (NKJV) are synonymous expressions. The “gift” of God may refer to His grace (Rom. 5:15) or to the Holy Spirit, through which God imparts that grace (Acts 2:38). Those who have “tasted” the Holy Spirit have experienced the “grace” of God, which includes the power to fulfill His will.

To taste “the goodness of the word of God” (Heb. 6:5, ESV) is to experience personally the truth of the gospel (1 Pet. 2:2, 3). “The powers of the age to come” refers to the miracles God will perform for believers in the future: resurrection (John 5:28, 29), transformation of our bodies, and eternal life. Believers, however, are beginning to “taste” these miracles in the present. They have experienced a spiritual resurrection (Col. 2:12, 13), a renewed mind (Rom. 12:2), and eternal life in Christ (John 5:24).

Paul probably has in mind the wilderness generation, who experienced the grace of God and His salvation. The wilderness generation was “enlightened” by the pillar of fire (Neh. 9:12, 19; Ps. 105:39), enjoyed the heavenly gift of manna (Exod. 16:15), experienced the Holy Spirit (Neh. 9:20), tasted the good word of God (Josh. 21:45), and saw “the powers of the age to come” in the “wonders and signs” performed in their deliverance from Egypt (Acts 7:36). Paul suggests, however, that just as the wilderness generation apostatized from God despite those evidences (Num. 14:1–35), the audience of Hebrews was in danger of doing the same despite all the evidences of God’s favor that they had enjoyed.

In Hebrews 6:7, the original text in Greek emphasizes the word “impossible.” It is impossible for God to restore those who have “fallen away” because “they are crucifying once again the Son of God” (Heb. 6:6, ESV). Paul wants to stress that there is no other way of salvation except through Christ (Acts 4:12). Salvation by any other means is as impossible as it is “for God to lie” (Heb. 6:18) or to please God “without faith” (Heb. 11:6).

To crucify again the Son of God is a figurative expression that seeks to describe something that happens in the personal relationship between Jesus and the believer.

When the religious leaders crucified Jesus, they did it because Jesus posed a threat to their supremacy and autonomy. Thus, they hoped to eliminate Jesus as a person and destroy a powerful and dangerous enemy. Similarly, the gospel challenges the sovereignty and self-determination of the individual at the most fundamental level. The essence of Christian life is to take up the cross and deny oneself (Matt. 16:24). This means to crucify “the world” (Gal. 6:14), the “old man” (Rom. 6:6), and “the flesh with its passions and desires” (Gal. 5:24, ESV). The purpose of the Christian life is that we undergo a kind of death. Unless we experience this death to self, we cannot receive the new life God wants to give us.

The struggle between Jesus and self is a struggle to the death (Rom. 8:7, 8; Gal. 5:17). It is a difficult battle that is not won at once. This passage does not refer to the person who sometimes fails in the battle against the “old man” and the “flesh.” Rather, it refers to the person who, after having experienced genuine salvation and what it implies (Heb. 6:4, 5), decides that Jesus is a threat to the kind of life he or she wants to have and moves to kill their relationship with Him. That is, as long as the person does not fully choose to turn away from Christ, there is still the hope of salvation.