Truly I tell you: This response is very strong. It is like an oath (a serious promise) and means something like, “[May God judge me] if I give this generation any such sign.” Such statements show firm and unchanging commitment (see Genesis 14:22–23; Numbers 32:10–11; Ruth 1:17; 1 Samuel 3:17; 20:13; 2 Samuel 3:35; 19:13).
Elsewhere, Jesus describes this generation as "adulterous and sinful" in Mark 8:38 and "unbelieving" in 9:19.