From
hustereo; a deficit; specially, poverty --
that which is behind
That which is behind of the afflictions of Christ - I have still some afflictions to pass through before my race of glory be finished; afflictions which fall on me on account of the Gospel; such as Christ bore from the same persecuting people....
....and fill up
that which is behind of the afflictions of Christ in my flesh; by
which are meant not the afflictions or sufferings of Christ in his own person; for these were all over, he was now entered into his glory, was exalted at the Father's right hand, and was crowned with glory and honour: there was nothing left behind of his sufferings, to be undergone by any of his people; he had drank of the cup and all the dregs of it; he had sustained the whole of his Father's wrath, and all the curses of the law, being abated nothing,
but was made perfect through sufferings; having perfectly suffered all, he suffered once and once for all, he will suffer no more; nor is there any need of his suffering more or again, for he has finished sin, wrought righteousness, made peace, and obtained eternal redemption; nor had he any partner in his sufferings, nor did he need any, or left any part of his sufferings to be filled up by others; for he endured all and the whole, which the law and justice of God could require in his own body, in the body of his flesh through death;
of these sufferings the apostle does not speak, but of such which he filled up in "his" own "flesh"; and design the afflictions of Christ in his members, which are called "his"...
Gill's
2 Peter 3
Final Words
14Therefore, beloved, since you are waiting for these, be diligent to be found by him without spot or blemish, and at peace.
15And count the patience of our Lord as salvation, just as our beloved brother
Paul also wrote to you according to the wisdom given him, 16as he does in all his letters when he speaks in them of these matters. There are some things in them that are hard to understand, which the ignorant and unstable twist to their own destruction, as they do the other Scriptures. 17You therefore, beloved, knowing this beforehand, take care that you are not carried away with the error of lawless people and lose your own stability.
18But grow in the grace and knowledge of our Lord and Savior Jesus Christ. To him be the glory both now and to the day of eternity. Amen.