Continuity is an important ingredient in comprehending the meaning of a treatise. The author mentions that they must "hold fast . . . firm until the end" (Heb 3:6,14). In previous sections of this paper the subjects addressed were assurance, hope, confidence and confession. The author cautions there must not be "an evil, unbelieving heart that falls away from the living God" (3:12 NASB) since "they were not able to enter because of unbelief" (:19). It is also translated a "sinful" (:12 NIV) "heart of unbelief" (:12 KJV). "Falls away" (:12) is also phrased as "in falling away." It is a "heart that turns away" (:12 NIV) and one "in departing from the living God" (:12 KJV). The Greek word for "falls away" is aphistemi meaning to lead away or to depart from being composed of apo meaning away from and histemi meaning to make a stand. The connotation is that it is a wilful, irretrievable act in the sense of a deliberate repudiation. If it were just a temporary decision without permanent ramifications it would be so non-consequential that being mentioned in the first place would be questionable.
They will "press on to maturity" (Heb 6:1) "if God permits" (:3). They are "those who" (:4) have experienced God's provision and "then have fallen away" (:6 NASB). The KJV translates it "if they shall fall away" and the NIV "if they fall away." That Greek word is parapito meaning to fall in, into or away and even to fail. It is composed of pipto meaning to fall and para designating from beside, by the side of, by or beside. But it does not define what has been rejected or disconnected from. However the five substantival participles are grouped together by the article tous which means "those who" (:4). The first four speak of spiritual characteristics so it is the environment that those people are experiencing. How serious is this "falling away?" The Old Testament equivalent is the word mahal meaning to act unfaithfully. It is used in Ezekiel 14:13 referencing, "'If a country sins against Me by committing unfaithfulness'" and in Numbers 5:12 by, "'If any man's wife goes astray and is unfaithful to him.'" In the latter it is a conscious turning her back on her husband which is why the word is translated "trespass." The word inherits the meaning of "completely turning away from" which qualifies it as defined as "apostasy." This would designate "fallen away" as more serious because the context is that "it is impossible to renew them again to repentance, since they again crucify to themselves the Son of God and put Him to open shame" (Heb 6:6). "It is worthless and close to being cursed, and it ends up being burned" (:8).
The act of the crucifixion "cancelled . . . the decrees against us . . . having nailed it to the cross" (Col 2:14). He gave "His life a ransom" (Mt 20:28) because that sacrifice was payment for our debt. Therefore he who recognizes and accepts this "'he must deny himself, and take up his cross daily and follow Me'" (Lk 9:23). That takes repentance. But those who "have fallen away" (Heb 6:6) repudiate that by unbelief. However, God will not permit certain things (:3). That is why it is not possible "to renew them again" (:6) because "they again crucify" (:6) Christ. God told Moses to "'strike the rock'" (Lev 17:6) but then he "struck the rock twice" (Nu 20:11) and because of this, he was not able to bring them "'into the land'" (:12). "If we go on sinning willfully . . . there no longer remains a sacrifice for sins" (Heb 10:26). We know it isn't just being "caught in any trespass" (Gal 6:1) because there is forgiveness. However, anyone "who does anything defiantly" (Nu 15:30) and "who has set aside the Law of Moses" (Heb 10:28) "shall be cut off from among his people" (Nu 15:30) and "'you shall not pity him'" (Dt 19:13) because treating the cross as just a common death is to repudiate that sacrifice. "Therefore let him who thinks he stands take heed that he does not fall" (1Co 10:12).