Reveal cards from the top of your deck until you reveal one costing 3 Coin or more. Put that card into your hand and discard the rest.
Sage is an Action card from Dark Ages. It is a cantrip that digs(dig) for a card costing 3 Coin or more; therefore it allows you to skip past your Copper, Curses(Curse), Estates(Estate), and Shelters(Shelter).