Growing up, I heard a number of sermons preached on Hebrews 12:1-2 – and rightly so, for it is a marvelous text:
Therefore, since we are surrounded by so great a cloud of witnesses, let us also lay aside every weight, and sin which clings so closely, and let us run with endurance the race that is set before us,  looking to Jesus, the founder and perfecter of our faith, who for the joy that was set before him endured the cross, despising the shame, and is seated at the right hand of the throne of God.
Generally, one of the major points of application in these sermons was based on the injunction “let us lay aside every weight.” “Weights” were contrasted with the following “sin,” and it was usually explained that this referred to things in our lives which were not intrinsically sinful, but which kept us from fully following Christ.
In studying this passage recently, however, it seemed odd to me that the writer would speak of “every weight” first, then “sin.” Moving from the lesser to the greater in this case did not appear to fit, because it involved moving from the less obvious category to the more obvious category. It seemed to me that it would fit better to say, “Let us lay aside (of course) sin which clings so closely, and (even go so far as to lay aside) every weight (as well).”
There is another understanding of the text, however, which avoids this difficulty, and appears to work better with the context as well. It seems preferable to understand the “and” (Greek και) between “weight” and “sin” in what is known as an “epexegetical” or “explanatory” sense, where the conjunction serves to lead into a further description or explanation of what precedes it. In the present text, that would read something like this: “Let us lay aside every weight, that is to say, let us lay aside sin, which clings so closely.”
If this understanding is correct, then the author is setting forth not two categories of things which are to be laid aside, but only one. “Every weight” and “sin which clings so closely” would be equivalent, with the latter explaining the former.
The context supports this understanding, in that the author is using an extended metaphor. The main clause of Hebrews 12:1-2 uses a picture of an athlete: “Let us run with endurance the race that is set before us.” Given that clear allusion, we should understand the phrase, “since we are surrounded by so great a cloud of witnesses” to have in view a Greek stadium, where a throng of spectators literally surrounded those competing in the games.
In the midst of these two athletic allusions, we find what appears to be a third: “let us lay aside every weight.” The verb “lay aside” (Gr. ἀποτίθημι) was used, even in the NT (Acts 7:58), to describe the removal of clothes. It is well known that Greek athletes competed in the nude, and while I doubt that the author of Hebrews approved of this practice, he appears to be drawing on it to build his extended metaphor. “Weight” (Gr. ὄγκος) is used only here in the NT and can as easily be translated as “encumbrance” or “impediment.” If it is correct to see a third athletic allusion, it should come as no surprise to find an explanation of it: “Lay aside every impediment, and by that I am referring to sin, which easily entangles us.”
As an aside, the “sin” here seems to be a general reference, not a particular one. The King James rendering “the sin which doth so easily beset us” has given rise to the term “besetting sin,” popularly understood as a specific sin which a believer finds particularly difficult to avoid. I do not deny that we each face particular temptations which are stronger for us than for others, nor do I deny that we are to lay aside sins which are a particular struggle for us. But if the author is equating “weight” with “sin,” we should notice the reference is to “every weight,” indicating he is thinking of sin in general. And sin in general, the author notes, easily entangles us. This is why we must lay it aside.
To take things a step further, the equation of “weight” and “sin” makes sense in that anything in which we participate which becomes more important to us than Christ (and thus impedes our progress in the Christian race) is itself sin. For instance, if I am so devoted to crossword puzzles that I begin to assign more value to them than I do to Jesus Christ, those crossword puzzles (though not intrinsically sinful) have become an idol to me. At that point, they are an impediment to running the race of faith, and need to be laid aside. As such, to continue to place the same value on those crossword puzzles would be to continue in sin. I do not deny that it is possible to put in one category entanglements which are intrinsically sinful, and to put in another category entanglements which are not intrinsically sinful. However, I don’t think the author of Hebrews is here thinking in those categories. We are to lay aside every sin, because sin is an impediment which easily entangles us.
(I should note that the understanding of “sin” to be equivalent to “weight” is found in Paul Ellingworth, The Epistle to the Hebrews, NIGTC (Eerdmans, 1993), 638.)
(As a point of interest, an even more extended athletic metaphor similar to Hebrews 12:1-2 is found in 4 Maccabees 17.11-16, in the author’s summarizing description of a Jewish mother and her seven sons who were martyred for not turning away from their Jewish heritage at the behest of the tyrant Antiochus Epiphanes. It is quite likely that the writer of Hebrews was familiar with 4 Maccabees, and that he had it in mind when he penned 11:35-38. Here is the pertinent passage from 4 Macc 17:
“Truly divine was the contest in which they were engaged. On that day virtue was the umpire and the test to which they were put was a test of endurance. The prize for victory was incorruption in long-lasting life. The first to enter the contest was Eleazar, but the mother of the seven sons competed also, and the brothers as well took part. The tyrant was the adversary, and the world and the life of men were the spectators. Piety won the victory and crowned her own contestants.”
Translation by H. Anderson in The Old Testament Pseudepigrapha (Doubleday, 1985), 2:562-63.)