ISB ~ 2 Corinthians 3 v5

our sufficiency is from God:Paul makes no claim to be qualified for apostleship apart from God’s grace (2:17). This is in marked contrast to the false apostles, who display their credentials with written documentation (3:1; 10:12).

• Paul is alluding to the call of Moses in the Greek version of Ex 4:10. Like Moses, who complains that his poor speaking ability makes him unfit to be a prophet, Paul sees himself as “unskilled in speaking” (2 Cor 11:6). Nevertheless, he is confident that the grace of God more than compensates for his personal weaknesses (12:9-10).

See word study:Unskilled at 2 Cor 11:6.