What is the meaning of "va'Yiktzav"?
Radak, Ralbag: He cut wood to the needed size (refer to 6:6:2:1-2 and the note there).
Why did Elisha cut new wood, and not simply cast the handle from which the blade came off?
Radak: Miracles are done with new matters. Similarly, he took a new flask [to put salt to cure the there of Yericho - 2:20]. He cut wood to be the handle of the blade that fell. The wood entered the hole in the blade, and the blade floated with [its new] handle.
Ralbag: Hashem did not make a miracle contrary to the nature of iron to sink, or wood to float 1 . Rather, Elisha cast the wood down forcefully, so naturally it would sink initially. He cut a big piece, so [when it miraculously entered the hole in the blade,] its 'force to float' would overpower the blade's force to sink, and together they would float 2 .
Kli Yakar citing Mahari, Malbim: This is wrong. We need not make miracles conform to nature!
I.e. the overall density (of the blade and handle together) would be less than that of water. E.g. if the wood was 80% as dense as water, and the iron 10 times as dense, if the wood is more than 50 times the volume of the blade, the overall density is less than that of water. (PF)
What is the meaning of "va'Ytzaf"?
Rashi: The saw floated on the water. Radak, Ralbag - with the new handle attached. 1
Radak #1: It is Po'el Omed (the Kli itself floated). It is unlike "Asher Hetzif Es Mei Yam Suf" (Devarim 11:4), which is Po'el Yotzei (Hashem made it float).
Radak: it is Po'el Yotzei (the Navi caused it to float).
Ralbag: [The wood] caused [the blade, now attached to it] to float.
Malbim: The iron alone floated, and the wood sank, both unlike their nature. 2
Kli Yakar: Mahari rejected this. Ha'Barzel implies that it was only the iron!
Kli Yakar: Why did the verse not mention that the wood sank? Also, there was no need for this miracle, only for the iron to float! (Perhaps the wood sank, lest people say that the water was extraordinarily dense, and this is why the blade floated. Some matters sink in normal water, but float in the Dead Sea, because its water is denser than normal! - PF)