
Well... Here is a translation from some notes taken by a member of my church when our pastor (who teaches from the Greek) exegeted this passage.
Here goes:
"I now rejoice in the sufferings on your behalf and fill up in turn the deficiency the things lacking with reference to the pressures of Christ in my flesh on behalf of His body . . . which is the church."
He is not speaking of suffering what Jesus did not suffer. He is speaking of needing to suffer because of the spiritual warfare resisting him, so he can take the deficiency of his congregation who lacked what he had to give to them (needing to be taught knowledge of Truth that they lacked).
Because of that need to fill up what was lacking, Paul was to experience the same kind of resistance that Christ suffered in the flesh when he was resisted by evil. Paul was sharing in the same type of sufferings Christ did. Why? Resistance of evil when the truth goes forth to claim new souls.
1 Peter 4:13 niv
"But rejoice that you participate in the sufferings of Christ, so that you may be overjoyed when his glory is revealed."
Paul was leading the way for others in sharing in the same type of suffering Jesus had experienced. Why? Because his congregatoin was lacking, having a deficiency, needing to grow in grace and truth.
For Paul to get them where they should be it required that he suffer pressures from evil. What was lacking was not suffering that Christ did not know. But what he needed to give them (truth) which required Paul to go through suffering to do so. Sufferings in his flesh like Christ experienced.
Romans 8:17 niv
"Now if we are children, then we are heirsheirs of God and co-heirs with Christ, if indeed we share in his sufferings in order that we may also share in his glory."
Those who did follow Paul's teaching also faced suffering of their own sufferings in being resisted by evil. That was part of Paul's suffering as well. To see others have to suffer in order to secure truth in their hearts. It required that Paul always encourage them, yet he himself needed to suffer until he could get them to reach maturity in Christ.
Galatians 4:19 niv
"My dear children, for whom I am again in the pains of childbirth until Christ is formed in you."
From what I have been taught, and from what I can recall..... that sounds about right to me.
1 Peter 2:21 niv
"To this you were called, because Christ suffered for you, leaving you an example, that you should follow in his steps."
Those who desire sound teaching will need to suffer in order to gain the truth they need to become strong in the Lord.
1 Peter 5:10 niv
"And the God of all grace, who called you to his eternal glory in Christ, after you have suffered a little while, will himself restore you and make you strong, firm and steadfast."
Paul was required not to suffer only for his own growth, like most of us do. But, also because of what was lacking in others. Those needing sound teaching.
Hope that helps.....
Grace and peace, GeneZ