After Jesus’ sermon in John 6, the Evangelist reported: “After this many of his disciples turned back and no longer walked with him” (John 6:66). Who were these disciples, as clearly they were not the Twelve whom Jesus addresses in verse 67? Luther’s thought is the commonly accepted idea today.
Very likely they [the disciples who abandoned Jesus after the John 6 sermon] took a large number of people with them. … In the Gospel of Luke 910:1ff.) we read that He sent out the seventy-two disciples to heal the sick, to preach, to work miracles, and to baptize in His name. From this we can infer that they were outstanding and surely not insignificant men; for they proclaimed the message of Christ, baptized, and wrought miracles. The fact that these men who had been so close to Christ deserted Him and took offense at His doctrine surely perplexed and bewildered the other people greatly. Luther’s Works, vol. 23, 186