How Was David Able to Lift Goliath's Sword?

A Bible Puzzle

In the biblical account of David’s showdown with Goliath, we are told that David was so small and skinny that he could barely walk while wearing King Saul’s armor, so he chose to go into battle without any.

So Saul clothed David with his armor, and he put a bronze helmet on his head; he also clothed him with a coat of mail. David fastened his sword to his armor and tried to walk, for he had not tested them. And David said to Saul, “I cannot walk with these, for I have not tested them.” So David took them off.
— 1 Samuel 17:38-39

In the same account we are told that Goliath was so enormous that his spear shaft was as thick as a weaver’s beam.

And a champion went out from the camp of the Philistines, named Goliath, from Gath, whose height was six cubits and a span. He had a bronze helmet on his head, and he was armed with a coat of mail, and the weight of the coat was five thousand shekels of bronze. And he had bronze armor on his legs and a bronze javelin between his shoulders. Now the staff of his spear was like a weaver’s beam, and his iron spearhead weighed six hundred shekels; and a shield-bearer went before him.

The Bible says that David used Goliath’s own sword to cut off his head. One must wonder, how did skinny David manage to do that?

The answer is that bronze is weaker than steel, and the maximum effective length for a bronze sword is a little over two feet. Goliath’s primary weapon was his enormous spear. He carried a short bronze sword on his belt like a dagger for self defense and for jobs like cutting off the heads of his enemies.

David probably could not have wielded Goliath’s spear. But Goliath’s sword was just the right size.