Cast not away therefore your confidence, which hath great recompence of reward. For ye have need of patience, that, after ye have done the will of God, ye might receive the promise. For yet a little while, and he that shall come will come, and will not tarry. Now the just shall live by faith: but if any man draw back, my soul shall have no pleasure in him.
It is important to notice that the verses preceding this warning (10:32-34) do not speak of superficial Christians who, as Jesus portrays in Lk 8:13, believe for a while and then fall away at the first provocation. Rather, they are described as “those who have received the light” (Greek: φωτισθεντες, used also in Hb 6:4 as “enlightened”), who “stood your ground in a great contest in the face of suffering,” “publicly exposed to insult and persecution,” “sympathized with those in prison,” and “joyfully accepted the confiscation of your property.” These are seasoned believers, yet they receive the same warnings against falling away as new Christians. The remaining verse of the chapter, Hb 10:39, “But we are not of those who shrink back and are destroyed, but of those who believe and are saved,” cannot be used to support the concept of eternal security. This would make no sense in light of what the previous verses just stated about the possibility of “shrinking back” (vr. 38), “throwing away your confidence” (vr. 35), and “punishment” for deserting the truth (vrs. 27-29). Hebrews 10:39 is simply a challenge to its hearers to remain a part of those who do not shrink back. It resembles the challenge in Hb 6:9, issued after warning them of the possibility of falling away from the Faith. He writes: “...we are confident of better things in your case—things that accompany salvation.” The challenge is to remain steadfast in the Faith and perform the works associated with salvation, while the warning is that no one is immune from falling away. (Robert A. Sungenis, Not By Bread Alone: The Biblical and Historical Evidence for the Eucharistic Sacrifice [2d ed.; State Line, Pa.: Catholic Apologetics International Publishing, Inc., 2009], 59-60 n. 55)