Who now rejoice in my sufferings for you, and fill up that which is behind of the afflictions of Christ in my flesh for his body's sake, which is the church:
Note 1 at Col 1:24: "THLIPSIS" is the Greek word that was translated as "afflictions" in this verse. It literally means "pressure" (Strong's Concordance). Afflictions, therefore, can be any pressures that come against us because of our stand for Christ.
Note 2 at Col 1:24: All of Christ's sufferings did not end when He finished His earthly ministry. He still takes the persecution of His people personally, as can be seen by His statement to Saul on the road to Damascus: "Saul, Saul, why persecutest thou me?" (Ac 9:4). He didn't ask Paul why he was persecuting His people. He said, "Why are you persecuting Me?" When we are persecuted for righteousness' sake, it is actually Christ who is being persecuted (see note 4 at Ac 9:4).
Therefore, Christ is still suffering persecution today when His people are persecuted and will continue to do so until the establishment of His physical kingdom. The persecutions that are still taking place today and will take place in the future are the afflictions that are yet to come that Paul was speaking of here.