St. John Chrysostom has something to say about the Gospel reading for today’s Mass. This is from s. 63.2 on the Gospel of Matthew (PG 58:605):
When the disciples were upset, he said, "With men this is impossible, but with God all things are possible." But why were the disciples upset since they were poor, in fact very poor? They were upset for others’ salvation and because the possessed great love toward them all. Already they were taking on the tenderness of teachers. At least they were in such trembling and fear for the whole world from Jesus’ declaration as to need much comfort.
And so after Jesus had made eye contact with them, he said, "With men this is impossible, but with God all things are possible." So with a pleasant and gentle look, he soothed those whose hearts were terrorized and relieved their anguish (for this is what the Evangelist meant by "looking at him"). Then he uplifted them with his words as he focused on the power of God, and thus he gave them faith.
If you also want to learn the way and how the impossible becomes possible, listen. He did not make this statement that what is impossible for man is possible for God merely so you could relax and do nothing and leave it all to God. No, he said this so you could understand the importance of calling upon God to give you help in this rigourous contest and that you might more readily approach his grace.