When I in Rome I often pop into the Church of San Luigi dei Francesi just to have a quick glance at the St. Matthew cycle by Caravaggio. I think right next to the church, so this is easy. One of the paintings is the great Calling of St. Matthew. It is a true masterpiece of its age.
The Fathers of the Church were also great masters of painting, word painting. They would explore the meaning of scenes in the Gospel, sculpting or sketching wonderful images for our minds.
Here is a brief riff by St. John Chrysostom on the calling of Matthew (Matthew 9:9), which is part of the Gospel reading for today’s Mass (in the Novus Ordo):
Why did Jesus not call Matthew at the same time as He called Peter and John and the rest? He came to each one at a particular time when He knew that they would respond to Him. He came at a different time to call Matthew when He was assured that Matthew would surrender to His call. Similarly, He called Paul at a different time when he was vulnerable, after the resurrection, something like a hunter going after his quarry. For He who is acquainted with our inmost hearts and knows the secrets of our minds knows when each one of us is ready to respond fully. Therefore He did not call them all together at the beginning, when Matthew was still in a hardened condition. Rather, only after countless miracles, after His fame was spread abroad, did He call Matthew. He knew Matthew had been softened for full responsiveness.
We may admire, incidently, the self-effacing temperament of Matthew, for we note how he does not disguise his own former life. In his account he freely adds his own name and his own bad profession, which the other Gospel writers had generously protected him under another name. But why did Matthew himself indicate precisely what the was "sitting at the tax office"? To point to the power of the One who called him, underscoring that the was being actively drawn away from the midst of the very evils in which he was presently engaged and that he had not already abandoned his wicked business as a tax gatherer. (Homliy 30.1 in NPNF 1 10:198-99)
God knew each one of us before the creation of the universe. He calls us into being at a sepcific point according to His plan. He wants us for Himself and gives us something to do according to His unfathomable design. Each one of us have moments when we are "ready" for this step, that move, some change of position or condition leading us to a new phase in our vocations.
The readiness is all.