This means renouncing evil and opening one's heart to letting the Holy Spirit be one's guide, the pope said April 1 during a live broadcast of his weekly general audience from the library of the Apostolic Palace.
The pope greeted people who were watching the broadcast, particularly those who had made arrangements long ago to attend the audience with their particular parish or group.
Among those who had been planning to attend was a group of young people from the Archdiocese of Milan, who instead were watching on social media.
The pope told them he could "almost sense your joyful and raucous presence" nonetheless, thanks to the "many written messages you have sent me; you have sent so many and they are beautiful," he said, holding in his hand a large number of printed pages.
"Thank you for this union with us," he said, reminding them to always live their faith "with enthusiasm and not lose hope in Jesus, a faithful friend who fills our life with happiness, even in difficult times."
The pope also recalled that April 2 would mark the 15th anniversary of the death of St. John Paul II. The pope told Polish-speaking viewers that during these "difficult days we are living through, I encourage you to trust in Divine Mercy and in the intercession of St. John Paul II."
In his main talk, the pope continued his series on the Eight Beatitudes by reflecting on the sixth beatitude, "Blessed are the clean of heart, for they will see God."
"To see God, you don't need to change your glasses or your vantage point or change theological authors who teach the way. What is needed is to free the heart from its deceptions. This is the only path," he said.
The disciples on the road to Emmaus did not recognize Jesus, because, as he told them, they were foolish and "slow of heart" to believe all that the prophets had said.
Being blind to Christ comes from a heart that is "foolish and slow," closed to the Spirit and content with one's own perceptions, the pope said.
"When we realize that our worst enemy often is hidden in our heart" then one experiences a "maturation" in faith. The most "noble" of battles, he said, is the one against the lies and deceptions inside oneself that lead to sin, he said.
"Sins change our inner vision, the evaluation of things, they make you see things that are not true or that at least are not 'that' true," he said.
Cleansing and purifying the heart, then, is a lifelong process of renunciation and liberating oneself from the evil inside one's heart, making room, instead, for the Lord. It means recognizing the ugly and evil parts inside oneself and letting one's life be led and taught by the Holy Spirit, he added.
Seeing God also means being able to see him in creation, how he is working in one's life, in the sacraments and in others, especially those who are poor and suffering, Pope Francis said.
"It is serious work and above all it is God at work in us -- during the trials and purifications of life -- that leads to great joy, and true and profound peace."
"Do not be afraid. Let us open the doors of our hearts to the Holy Spirit so he may cleanse them" and ultimately lead people to the fullness of joy and peace in heaven.