Isaiah in the Temple, Peter in the fishing boat, and Paul writing to his beloved Corinthians—what do they have in common? Each of this Sunday's three readings reflects on their experience of being commissioned as servants of God. As different as these three situations are—a Hebrew prophet in the Solomonic Temple, a Galilean fisherman surprised by an enormous catch, and a Greek-writing Pharisee reflecting on being a Christian convert—the three scenarios have startlingly similar elements.

Each of these men is confronted by an awesome manifestation of divine power. Isaiah of Jerusalem has a vision that he can only call “seeing the Lord.” Celestial beings called Seraphim (literally “burning ones”) sing the praise that we have incorporated into our Eucharistic Prayer: “Holy, holy, holy is the Lord of hosts! All the earth is filled with his glory!” Thus the prophet comes to know God, not just as a local Near Eastern divinity but as the God of all, the one whose glory is shown in all creation. This becomes a major theme for this prophet and the successors who speak in his name: Yahweh, the creator of all, is the redeemer of Israel.

For Peter, the awesome manifestation of the divine comes in the form of an amazingly abundant catch after a night of fruitless toil. As in the wine-sign at Cana, a surprising abundance follows obedient response to the command of Jesus.

In the presence of the divine manifestation, all three feel a profound unworthiness. “Woe is me,” says Isaiah. “I am doomed! For I am a man of unclean lips, living among a people of unclean lips; yet my eyes have seen the King, the Lord of Hosts!” Peter's reaction to the titanic catch is to fall at Jesus' knees and say, “Depart from me. Lord, for I am a sinful man.” As for Paul, when he reflects on his experience, he can only say, “I am the least of the apostles, not fit to be called an apostle, because I persecuted the church of God.”

In each case, what followed that sense of unworthiness was a divine assurance and—the biggest surprise of all—a commission. One of the “burning ones” touches Isaiah with an ember and assures him that his wickedness is purged. Then the future prophet hears the voice of the Lord asking for a volunteer. The amazed and kneeling Peter hears Jesus address him, “Do not be afraid; from now on you will be catching men.”

For his part, Paul found himself drawn into a mission of surprising fruitfulness (amazingly effective among Gentiles rather than among his fellow Jews). When he alludes to this mission as he writes to the Corinthians, he is compelled to say, “But by the grace of God I am what I am, and his grace to me has not been ineffective. Indeed, I have toiled harder than all of them; not I, however, but the grace of God that is with me.” (1 Cor 15:10)

Clearly, in this pattern of the calls of Isaiah, Peter, and Paul, there is a message for all of us. We who find ourselves blessed with a sense of divine presence inevitably feel a sense of unworthiness in proportion to our sense of God's goodness. But God does not allow us to stay there. Along comes the purifying ember (God healing in us what we are unable to fix) and then some sense of a task, as if to say: “Forget about your unworthiness, I have a job for you to do; get up and do what needs to be done, and I'll see that you get the support you need.”

What does it take to be ready for the divine manifestation in the first place? Isaiah was worshiping in the Temple. Peter was plying his trade and alert to the Master's suggestion. And Paul, even as he was persecuting what he later recognized to be “the church of God,” was following his best lights, zealous for God.

The systematic theology of grace and human freedom may be complicated, but these stories of calling give us all the ingredients.