On that day he said, “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.”
If Salem, the place of which Melchizedec was king, was Jerusalem (as seems probable from Psa 76:2), it was famous in Abraham's time. Joshua, in his time, found it the chief city of the south part of Canaan, Jos 10:1-3. It fell to Benjamin's lot (Jos 18:28), but joined close to Judah's, Jos 15:8.
Commenting on 2 Samuel 5:6-10
And David said on that day,.... On which he took the strong hold of Zion: whosoever getteth up to the gutter; where it is generally supposed the blind and lame were, whether images or real men: but what is meant by "Tzinnur", we render "gutter", is not easy to say; we follow some of the Jewish writers, who take it to be a canal, or...
Whosoever getteth up to the gutter--This is thought by some to mean a subterranean passage; by others a spout through which water was poured upon the fire which the besiegers often applied to the woodwork at the gateways, and by the projections of which a skilful climber might make his ascent good; a third class render the words, "whosoever dasheth them against the precipice" (Ch1 11:6).