ROME — Pope Francis apologized for Catholic mistreatment of other Christian traditions Monday, and called on Catholics to forgive followers of those traditions for any offenses of “today and in the past,” as a step toward deeper unity.

“As Bishop of Rome and Shepherd of the Catholic Church, I plead for mercy and forgiveness for non-evangelical behaviors by Catholics against Christians of other churches,” Francis said, referring to conduct not in keeping with the Gospel of Christ.

“We cannot undo what was done in the past, but we don’t want to allow the weight of past sins to pollute our relationships,” he said. “The mercy of God will renew our relations.”

The pope’s comments came during a multi-denominational vespers service in the Basilica of St. Paul Outside the Walls in Rome. As is tradition, the service was celebrated to mark the feast of the Conversion of St. Paul and also the close of the annual Week of Prayer for Christian Unity, which runs each year from Jan. 18 to 25.

Representatives of various Christian churches present in Rome, such as Anglicans, Orthodox, and Pentecostals, participated in the service.

The pope called for the denominations to ask “above all the forgiveness for the sin of our division, an open wound in the Body of Christ.”

This is not the first time Francis has asked forgiveness for Catholic persecution of other Christian churches. In 2014, during a visit with a Pentecostal leader, he apologized in the name of the Church for the persecution of this burgeoning movement.

On Monday, the pontiff also appealed for Christians to recognize that beyond the differences that still divide those who follow Jesus, in the origin of Christian life there’s a call made by God himself.

“We will move forward on the road to full visible communion among Christians not only when we get closer to one another, but especially when we are converted to the Lord, that by his grace chooses us and calls us to be his disciples,” Francis said, adding that “it’s not only the call which unites us, but we [also] share the same mission: to proclaim the wonderful works of God.”

The pope then called for Christian churches to work together spreading the Gospel even as they work to achieve full communion.

“Walking and working together, we [will] realize that we are already united in the name of the Lord,” Francis told those who packed the Roman basilica.

As with the other three major basilicas in Rome, St. Paul Outside the Walls has a Holy Door that was thrown open for the pope’s special Holy Year of Mercy. At the beginning of Monday’s ceremony, Francis, together with Metropolitan Gennadios representing the Ecumenical Patriarchate, and Bishop David Moxon from the Anglican Church, walked through the door together.

This gesture, Francis said, was meant as a reminder that the only door leading to salvation is Jesus, “the merciful face of the Father.”

As a final note, the pope called for all those present to pray for unity, knowing that the “humble request” is sustained by the intercession and the example of the multitude of Christian martyrs “of yesterday and today,” who reflect what he has described repeatedly as an “ecumenism of blood.”