A.T. Robertson Commentary 1 Corinthians 8:12

"And thus, sinning against the brethren, and wounding their conscience when it is weak, ye sin against Christ." — 1 Corinthians 8:12 (ASV)

Wounding their conscience (τυπτοντες αυτων την συνειδησιν). Old verb τυπτω, to smite with fist, staff, whip. The conscience is sensitive to a blow like that, a slap in the face.

Ye sin against Christ (εις Χριστον αμαρτανετε). That fact they were overlooking. Jesus had said to Saul that he was persecuting him when he persecuted his disciples (Acts 9:5). One may wonder if Paul knew the words of Jesus in Mt 25:40, "ye did it unto me."