The Apostle has been telling us (1) that within the Christian circle there are some marked by envy, strife, and contention; (2) that all seek their own, not the things which are Jesus Christ's; (3) that many walk in such a way that they are the enemies of the cross of Christ. Alas! these things are still found among the people of God, and may well call forth sorrow and tears, even as they did with him.
But the Apostle tells us more; he not only looks abroad and sees the failure of the saints, but he looks up and sees the glory of Jesus. He sees Christ in the glory, the prize of the calling on high (3:14). He sees that God has called us to be with Christ and like Christ in glory, and he sees the blessed end of the wilderness journey with all its sorrows and failure. With this glorious end in view, he forgets the things that are behind and presses on to the goal.
Moreover he not only looks up to Christ in the glory, but he looks for the coming of the Lord Jesus Christ to change our bodies of humiliation into bodies of glory. Looking around he may weep, but looking up, and looking on, he rejoices, and exhorts us to "Rejoice in the Lord alway."
We cannot rejoice in ourselves, our service, or our walk: we cannot always rejoice in our circumstances or in the saints. But with the living Christ on high, and the coming Christ before us, we can "Rejoice in the Lord alway."