Text in red are my additions.
Heb 12:1 Let us then, since we have such a cloud of witnesses about us, set aside every encumbrance and the sin which enmesheth us, and run on enduringly the course which still lies before us,
All the history of Israel furnishes us a lesson, and sets a model before us. Like the ancient Jews, the Christian is inclined to murmur. This tendency, he must put aside, and follow in all things his leader Jesus. If Jesus took no heed of the shame. He had to endure, the Christian should have strength and courage to bear his small trials.
The ‘cloud’ suggests the immensity of the multitude of witnesses. ‘Witness’ means here one who, tells what he has experienced. The Christian life is conceived here in true Pauline fashion as a contest in the arena. All encumbrances that would impede us in the race of the Christian life must be cast aside, and our whole energy should be bent on securing victory in the contest.
ογκον (ogkon) means a burden. ευπεριστατον (euperistaton) is uncertain in meahiftg. Chrysostom takes it as = ‘encompassed’, ‘surrounded’. The text suggests that sin is a sort of heavy or awkward garment that impedes movement. Apparently there is present also the thought of sin as a mesh.
And run on, etc. τρεχωμεν (trechomen) obviously refers to a contest in running. The Christian cannot shirk the contest; it is his life. Nor must he merely begin it; he must carry it through. Jesus supplies the motive and the source of strength for the race. He is the model of faith under trial: He is also the model of the faith which persists to the end.
Heb 12:2 looking towards the Leader and Consummator of faith, Jesus, who, for the sake of the joy that lay before Him, endured the cross, and heeded not shame, and hath taken His seat at the right hand of the throne of God.
The phrase for the sake of the joy that lay before him (αντι της προκειμενης αυτω χαρας = anti tes prokeimenes auto charas) is usually explained by the Greek Fathers as meaning that Jesus set aside the glory and happiness which were His right, in order to take up the cross. Others take the joy as the future blessedness which Jesus would enjoy as a reward for His endurance of the cross. The joy would be thus, in a sense, the athlete’s reward. αντι in this view, would mean ‘for the sake of ‘. Cf. Philippi 2:5 ff.
Heb 12:3 Consider then Him who hath endured such a grievous opposition of sinners against Himself, so that ye may not grow weary and lose heart.
The readers’ should estimate their own difficulties by comparing them with those of Jesus. He had to bear an opposition of sinners which He had nowise deserved. The αντιλογιαν (antilogian = “opposition”) found its final expression in the Crucifixion. Note how the idea of an athletic context appears at the end of verse 3.
Heb 12:4 Ye have not’ yet resisted unto blood in the struggle with sin,
The reference to resistance to blood may mean that no serious persecution has yet broken out against them. Or the sense may he that their struggle with sin has not been really severe.