12:12-17 A burden of affliction is apt to make the Christian's hands hang down, and his knees grow feeble, to dispirit him and discourage him; but against this he must strive, that he may better run his spiritual race and course. Faith and patience enable believers to follow peace and holiness, as a man follows his calling constantly, diligently, and with pleasure. Peace with men, of all sects and parties, will be favourable to our pursuit of holiness. But peace and holiness go together; there can be not right peace without holiness. Where persons fail of having the true grace of God, corruption will prevail and break forth; beware lest any unmortified lust in the heart, which seems to be dead, should spring up, to trouble and disturb the whole body. Falling away from Christ is the fruit of preferring the delights of the flesh, to the blessing of God, and the heavenly inheritance, as Esau did. But sinners will not always have such mean thoughts of the Divine blessing and inheritance as they now have. It agrees with the profane man's disposition, to desire the blessing, yet to despise the means whereby the blessing is to be gained. But God will neither sever the means from the blessing, nor join the blessing with the satisfying of man's lusts. God's mercy and blessing were never sought carefully and not obtained.

15. lest any … fall—Greek, "lest any (namely, through sloth in running) failing," or "falling short of the grace of God … trouble you." The image is taken from a company of travellers, one of whom lags behind, and so never reaches the end of the long and laborious journey [Chrysostom].

root of bitterness—not merely a "bitter root," which might possibly bring forth sweet fruits; this, a root whose essence is "bitterness," never could. Paul here refers to De 29:18, "Lest there should be among you a root that beareth gall and wormwood" (compare Ac 8:23). Root of bitterness comprehends every person (compare Heb 12:16) and every principle of doctrine or practice so radically corrupt as to spread corruption all around. The only safety is in rooting out such a root of bitterness.

many—rather, "the many," that is, the whole congregation. So long as it is hidden under the earth it cannot be remedied, but when it "springs up," it must be dealt with boldly. Still remember the caution (Mt 13:26-30) as to rooting out persons. No such danger can arise in rooting out bad principles.