There are those it has been reported who believe that cross was a symbolism added to the faith later by Constantine. Paul is not explaining a symbolism here, he is describing his key life principal. Whether he wore or prayed to a cross is of secondary consequence.
I have heard theories that Paul may have been crippled or have a deformity in arm or hand. We have already summized that he could well have problems with his eye sight. We also know that he was beaten and stoned near to death on several occasions and therefore be severely damaged. The Galatians here would have been deeply moved by whatever this sentence points to; he does bear the marks of Christ.
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