"Be Ye Perfect" :

"When people say that it is impossible to attain perfection, to be once and for all free from the passions, or to participate fully in the Holy Spirit, we should cite Holy Scripture against them, showing them that they are ignorant and speak falsely and dangerously. For the Lord said: 'Become perfect, as your heavenly Father is perfect' (Matt. 5:48)..."

St. Makarios of Egypt (The Homilies, II: Prayer nos. 29, The Philokalia
Vol. 3 edited by Palmer, Sherrard and Ware; Faber and Faber pg. 296)