Exodus 29:33 explicitly prohibits a layman from eating holy things, directly showing why David's action was exceptional.

Leviticus 24:5-9 gives the institution of the showbread that David ate, defining it as holy and for priests only.

Leviticus 24:9 repeats the command that only Aaron and his sons may eat the showbread in a holy place — the specific restriction.

1 Samuel 21:1 recounts David's visit to Ahimelech where he took the consecrated bread — the very event Jesus references.

Matthew 12:3 is the parallel account of Jesus citing David's action, confirming the same teaching.

Luke 6:3 is the parallel account in the third Gospel, reinforcing the same argument.

Exodus 29:32 describes the priestly eating of consecrated bread, establishing the law that only priests could eat holy bread — the law David broke.

1 Samuel 22:20-22 recounts Abiathar's escape from the massacre at Nob, explaining how he became David's priest — context for Mark naming him high priest.

1 Samuel 23:6 says Abiathar brought the ephod to David, linking him to priestly items — relevant to the consecrated bread incident.

2 Samuel 20:25 lists Abiathar as priest in David's administration — directly confirms his high priest status referenced in Mark.

1 Kings 4:4 lists Abiathar as priest again, reinforcing his high priest role — supports Mark's designation.