Mark 8:12

The Greek word translated "sighing deeply" is anastenazo.

"It describes Jesus’ grief and disappointment when faced with the unbelief of those who, because of their spiritual privileges, ought to have been more responsive to him." [Note: Wessel, p. 688.]

The spirit was Jesus’ human spirit. The contemporary Jews who opposed Jesus constituted the generation to which He referred. He refused to give the type of sign they requested because the evidence that He had presented was more than adequate to convince an open-minded person. Jesus distinguished between miracles (Gr. dynamis) and signs (Gr. semeion) by using the second word here. He had given plenty of miracles to bolster faith. He would not give a sign to those bent on disbelieving. From this Mark’s readers were to learn that Jesus’ miracles were ample proof of His deity.