{Henceforth} (apo tou nun). From the time that we gained
this view of Christ's death for us. {After the flesh} (kata
sarka). According to the flesh, the fleshy way of looking at
men. He, of course, knows men "in the flesh (en t(8869) sarki), but
Paul is not speaking of that. Worldly standards and distinctions
of race, class, cut no figure now with Paul ( Ga 3:28 ) as he
looks at men from the standpoint of the Cross of Christ. {Even
though we have known Christ after the flesh} (ei kai egn(936b)amen
kata sarka Christon). Concessive clause (ei kai, if even or
also) with perfect active indicative. Paul admits that he had
once looked at Christ kata sarka, but now no longer does it.
Obviously he uses kata sarka in precisely the same sense that
he did in verse  15  about men. He had before his conversion
known Christ kata sarka, according to the standards of the men
of his time, the Sanhedrin and other Jewish leaders. He had led
the persecution against Jesus till Jesus challenged and stopped
him ( Ac 9:4 ). That event turned Paul clean round and he no
longer knows Christ in the old way kata sarka. Paul may or may
not have seen Jesus in the flesh before his death, but he says
absolutely nothing on that point here.