What does “forgetting what is behind” mean in Philippians 3:13?

I--whatever others count as to themselves. He who counts himself perfect, must deceive himself by calling sin infirmity (Jo1 1:8); at the same time, each must aim at perfection, to be a Christian at all (Mat 5:48). forgetting those things . . . behind--Looking back is sure to end in going back (Luk 9:62): So Lot's wife (Luk 17:32). If in stemming a current we cease pulling the oar against it, we are carried back. God's word to us is as it was to Israel…

…Again, Brethren, I count not myself to have apprehended (Phi 3:13), ou logizomai. "I make this judgment of the case; I thus reason with myself." Observe, Those who think they have grace enough give proof that they have little enough, or rather that they have none at all; because, wherever there is true grace, there is a desire of more grace, and a pressing towards the perfection of grace. (2.) What the apostle's actings were under this conviction. Considering that he had not already attained…

Brethren, I count not myself to have apprehended,.... That for which he was apprehended of Christ: he had not attained to perfect knowledge, was not come to the mark, had not received the prize, or laid hold on eternal life; though he had received so much grace, and such gifts, as had qualified him for an apostle; and he had been so many years in that office, and had so great a knowledge in the mystery of the Gospel, and had laboured in it more abundantly than others, and with great success…