Philippians 3:8 (ESV) … “Indeed, I count everything as loss because of the surpassing worth of knowing Christ Jesus my Lord. For his sake I have suffered the loss of all things and count them as rubbish, in order that I may gain Christ…”
Yea, doubtless, and I count all things but loss. Not only those things which he had just specified, and which he had himself possessed, he says he would be willing to renounce in order to obtain an interest in the Saviour, but every thing which could be imagined. Were all the wealth and honour which could be conceived of his, he would be willing to renounce them in order that he might obtain the knowledge of the Redeemer. He would be a gainer who should sacrifice every thing in order to win Christ. Paul had not only acted on this principle when he became a Christian, but had ever afterwards continued to be ready to give up every thing in order that he might obtain an interest in the Saviour. He uses here the same word—ζημίαν—which he does in the Acts of the Apostles, chap. 27:21, when speaking of the loss which had been sustained by loosing from Crete, contrary to his advice, on the voyage to Rome. The idea here seems to be, “What I might obtain, or did possess, I regard as loss in comparison with the knowledge of Christ, even as seamen do the goods on which they set a high value, in comparison with their lives. Valuable as they may be, they are willing to throw them all overboard in order to save themselves.” Burder, in Ros. Alt. u. neu. Morgenland, in loc.
For the excellency of the knowledge. A Hebrew expression to denote excellent knowledge. The idea is, that he held everything else to be worthless in comparison with that knowledge, and he was willing to sacrifice everything else in order to obtain it. On the value of this knowledge of the Saviour, see Notes on Eph. 3:19.
For whom I have suffered the loss of all things. Paul, when he became a Christian, gave up his brilliant prospects in regard to this life, and everything indeed on which his heart had been placed. He abandoned the hope of honour and distinction; he sacrificed every prospect of gain or ease; and he gave up his dearest friends and separated himself from those whom he tenderly loved. He might have risen to the highest posts of honour in his native land, and the path which an ambitious young man desires was fully open before him. But all this had been cheerfully sacrificed in order that he might obtain an interest in the Saviour, and partake of the blessings of his religion. He has not, indeed, informed us of the exact extent of his loss in becoming a Christian. It is by no means improbable that he had been excommunicated by the Jews; and that he had been disowned by his own family.
And do count them but dung. The word here used—σκύβαλον—occurs nowhere else in the New Testament. It means, properly, dregs; refuse; what is thrown away as worthless; chaff; offal, or the refuse of a table or of slaughtered animals, and then filth of any kind. No language could express a more deep sense of the utter worthlessness of all that external advantages can confer in the matter of salvation. In the question of justification before God, all reliance on birth, and blood, and external morality, and forms of religion, and prayers, and alms, is to be renounced, and, in comparison with the merits of the great Redeemer, to be esteemed as vile. Such were Paul’s views, and we may remark that if this was so in his case, it should be in ours. Such things, can no more avail for our salvation than they could for his. We can no more be justified by them than he could. Nor will they do anything more in our case to commend us to God than they did in his.
 Barnes, A. (1884–1885). Notes on the New Testament: Ephesians, Philippians & Colossians. (R. Frew, Ed.) (pp. 194–195). London: Blackie & Son.