Sotah 39a: A Kohen who did not wash his hands may not bless - "lift your hands in Kedushah and bless Hashem."

Radak #1: Lift your hands, i.e. give Birkas Kohanim, in a Kodesh place.

Radak #2: Lift your hands in Tefilah, like "Nisa Levavenu El Kapayim" (Eichah 3:41), i.e. [we will lift our hearts] with our hands. Perhaps "Kodesh" is towards the Kodesh place, like "El Dvir Kadshecha" (28:2).

Malbim: The author depicts like people who bless - they raise their hands and put them on the head of the one who is blessed - "va'Yisa Aharon Es Yadav El ha'Am" (Vayikra 9:22). However, here does not discuss physical hands, rather, Kodesh hands. The verse depicts Kedushah as an entity; it lifts its hands and blesses Hashem b'Kodesh - to Kodshei Kodoshim, i.e. through conduct in Kedushah. Kedushah is overpowering physicality and its nature, and conducting based on intellect.