At a bris, we say 'this katten will become a gadol.'(ze hakatan gadol yihiyeh'. What does that mean? I heard (on a tape by Rabbi Krohn in the name of one of the Rabbi Soloveitchiks) the following nice vort... The Gra (others say it in the name of R Tzaddok) says that the true meaning of any given word lies in the first time it appears in the Torah.

So, let's see... Kattan and Gadol first appear in the Torah in bereishis (1;16) regarding the creation of the sun and moon. The Sun is called the 'ma'or hagadol (the big light) and the moon is 'hamaor hakatan' (the small light). Using this, we can now understand that cryptic line in the bris; we are blessing that the child will turn from a kattan to a gadol. We are blessing that the child should develop from the moon; who has none of its own light and can just reflect the light of the Sun, into a 'gadol' ie a Sun; someone who has light of his own to add and shine into the world. (And 'ki ner mitzvah vetorah ohr')