“learning” = “letters” (KJV) = (gramma) = the letters formed. This can mean a letter or epistle, or the sacred Scriptures. It was used by the Greeks to indicate learning and in this case probably refers to a religious knowledge, or a knowledge of scripture.

“The marvel was that Jesus showed Himself familiar with the literary methods of the time, which were supposed to be confined to the scholars of the popular teachers.” (Westcott). “It is not the wisdom of Jesus that disconcerted the Jewish leaders, but his learning (Marcus Dods). And yet Jesus had not attended either of the rabbinical theological schools in Jerusalem (Hillel, Shammai). He was not a rabbi in the technical sense, only a carpenter, and yet he surpassed the professional rabbis in the use of their own methods of debate. It is sometimes true today that unschooled men in various walks of life forge ahead of men of lesser gifts with school training. See the like puzzle of the Sanhedrin concerning Peter and John (Acts 4:13). This is not an argument against education, but it takes more than education to make a real man. Probably this sneer at Jesus came from some of the teachers in the Jerusalem seminaries.” (RWP) The irony is that the very Logos of God is being treated by these pride-filled Jews as an uneducated fellow.

Acts 4:13  When they saw the courage of Peter and John and realised that they were unschooled, ordinary men, they were astonished and they took note that these men had been with Jesus.

Their words betrayed what was in their hearts. It was not their consciences that were convicted, but their curiosity that was aroused. They had carnal thoughts and were not honestly seeking God. They were more interested in the delivery than in the message itself. The most powerful sermon ever delivered this side of Christ may have been “Sinners in the Hand of an Angry God” by Jonathan Edwards, and yet his delivery was a monotone reading of the text. How we preach has nothing to do with the power of God. What has to do with God is the content of what we preach and its impact on the lives of our listeners.