"'I am the good shepherd. I know my own – by which I mean, I love them – and my own know me.' In plain words: those who love me are willing to follow me, for anyone who does not love the truth has not yet come to know it. My dear brethren, you have heard the test we pastors have to undergo. Turn now to consider how these words of our Lord imply a test for yourselves also. Ask yourselves whether you belong to his flock, whether you know him, whether the light of his truth shines in your minds. I assure you that it is not by faith that you will come to know him, but by love; not by mere conviction, but by action. John the evangelist is my authority for this statement. He tells us that 'anyone who claims to know God without keeping his commandments is a liar.' Consequently, the Lord immediately adds: As the Father knows me and I know the Father; and I lay down my life for my sheep. Clearly he means that laying down his life for his sheep gives evidence of his knowledge of the Father and the Father’s knowledge of him. In other words, by the love with which he dies for his sheep he shows how greatly he loves his Father."
-St. Gregory the Great