Though I might also have confidence in the flesh - That is, though I had uncommon advantages of this kind; and if anyone could have trusted in them, I could have done it. The object of the apostle is to show that he did not despise those things because he did not possess them, but because he now saw that they were of no value in the great matter of salvation. Once he had confided in them, and if anyone could find any ground of reliance on them, he could have found more than any of them. But he had seen that all these things were valueless in regard to the salvation of the soul. We may remark here, that Christians do not despise or disregard advantages of birth, or amiableness of manners, or external morality, because they do not possess them - but because they regard them as insufficient to secure their salvation. They who have been most amiable and moral before their conversion will speak in the most decided manner of the insufficiency of these things for salvation, and of the danger of relying on them. They have once tried it, and they now see that their feet were standing on a slippery rock. The Greek here is, literally: "although I((was) having confidence in the flesh." The meaning is, that he had every ground of confidence in the flesh which anyone could have, and that if there was any advantage for salvation to be derived from birth, and blood, and external conformity to the law, he possessed it. He had more to rely on than most other people had; nay, he could have boasted of advantages of this sort which could not be found united in any other individual. What those advantages were, he proceeds to specify.

Philippians 3:4 Parallel Commentaries

Laid Hold of and Laying Hold
'I follow after if that I may apprehend that for which also I was apprehended of Christ Jesus.'--PHIL. iii. 12. 'I was laid hold of by Jesus Christ.' That is how Paul thinks of what we call his conversion. He would never have 'turned' unless a hand had been laid upon him. A strong loving grasp had gripped him in the midst of his career of persecution, and all that he had done was to yield to the grip, and not to wriggle out of it. The strong expression suggests, as it seems to me, the suddenness …
Alexander Maclaren—Expositions of Holy Scripture

Do You Know Him?
Have I imagined emotions which would not be natural? I think not. The most cool and calculating would be warmed with desires like these. Methinks what I have now pictured before you will wake the echoes in your breasts, and you will say, "Ah, it is even so! It is because Christ loved me and gave himself for me that I want to know him; it is because he has shed his blood for me and has chosen me that I may be one with him for ever, that my soul desires a fuller acquaintance with him." Now may God, …
Charles Haddon Spurgeon—Spurgeon's Sermons Volume 10: 1864

The Power of Christ Illustrated by the Resurrection
Beloved, how intimately is the whole of our life interwoven with the life of Christ! His first coming has been to us salvation, and we are delivered from the wrath of God through him. We live still because he lives, and never is our life more joyous than when we look most steadily to him. The completion of our salvation in the deliverance of our body from the bondage of corruption, in the raising of our dust to a glorious immortality, that also is wrapped up with the personal resurrection and quickening …
Charles Haddon Spurgeon—Spurgeon's Sermons Volume 17: 1871