“The blind and the lame”
Whoever attacks the Jebusites must use the water shaft to reach the lame and blind who are despised by David. That is why it is said, 'The blind and the lame will never enter the palace.' (2 Samuel 5:8 BSB)
What it sounds like today
A confusing, seemingly cruel remark about disabled people.
The cultural key
This is one of the hardest verses in Samuel to untangle. The Jebusites held the fortress of Jerusalem and taunted that it was so impregnable even the blind and the lame could man its walls. David's answer was to bypass the walls entirely, apparently going up the 'water shaft' to take the citadel from within. The details stay uncertain: tsinnor is a rare word (usually rendered 'water shaft,' but read by some as 'grappling hook' or even 'windpipe'), and whether the route was Jerusalem's Warren's Shaft is debated among archaeologists. The exchange spawned a local proverb about 'the blind and the lame,' and the capture gave David his capital, thereafter called the City of David.
Recovered meaning
The Jebusites' boast about blind-and-lame defenders is answered by a daring infiltration up the water tunnel, and David wins his capital. The obscure taunt froze into a proverb, and the fortress became Jerusalem, the City of David.