God ‘tested Abraham’ (cf. Gen. 22:1-14), that is, God afflicted him for his own benefit, not in order to learn what kind of man Abraham was – for He knew him, since He knows all things before they come into existence – but in order to provide him with opportunities for showing perfect faith.
St. Mark the Ascetic, “On the Spiritual Law: Two Hundred Texts” No. 203, The Philokalia: The Complete Text (Vol. 1)