I have posted RSRH's commentary on Bamidbar 6: 23 - 27 at http://www.stevens.edu/golem/llevine/rsrh/birkas_kohanim.pdf In his commentary Rav Hirsch gives many insights in Birkas Kohanim and explains the differences in the way Birkas Kohanim is done today and how it was done in the Bais Hamikdash. He provides reasons for these differences. Yitzchok Levine