Here is a brief intro plus a picture.
watch?v=cZe28F1XYxc
Τὸ γὰρ μὴ παρέργως ἀκούειν τῶν θεολογικῶν φωνῶν, ἀλλὰ πειρᾶσθαι τὸν ἐν ἑκάστῃ λέξει καὶ ἐν ἑκάστῃ συλλαβῇ κεκρυμμένον νοῦν ἐξιχνεύειν, οὐκ ἀργῶν εἰς εὐσέβειαν, ἀλλὰ γνωριζόντων τὸν σκοπὸν τῆς κλήσεως ἡμῶν· ὅτι πρόκειται ἡμῖν ὁμοιωθῆναι Θεῷ, κατὰ τὸ δυνατὸν ἀνθρώπου φύσει.
~ St. Basil the Great, On the Holy Spirit1.2