We proclaim it at every Mass and sing it in many of our hymns. This song of praise can be so familiar to us, however, that we may not think much about it. What does it mean to call God holy? And why do we sing it so often?

The Sanctus (Latin for “holy”) is an ancient hymn that has its roots in the worship of our Jewish brothers and sisters. Like them, we believe that when we sing this hymn, we are joining all the angels in heaven as they praise the holiness and glory of our God. But the Sanctus is even older than the Jewish synagogue service. It comes from a vision that the prophet Isaiah had in the eighth century BC.

As he was praying in the Temple one day, Isaiah saw something he never expected: a vision of God himself. In the midst of the smoke from the incense, he saw the Lord enthroned in heavenly glory and surrounded by angels who cried out, “Holy, holy, holy is the Lord of hosts!” (Isaiah 6:3). The angels’ worship was so powerful that it shook the Temple to its foundations.

That vision changed Isaiah’s life. He saw the “otherness,” the power, and the majesty of God, and he was undone. Compared to the holiness of God, Isaiah felt “doomed.” He knew that he was “a man of unclean lips, living among a people of unclean lips” (Isaiah 6:5). But this holy God was also merciful. He sent a seraph to cleanse Isaiah from his sins. The experience was so moving that when God asked, “Whom shall I send?” Isaiah eagerly responded, “Here I am; send me!” (6:8).

Isaiah’s vision reveals the great mystery of a holy God who wants to have a relationship with human beings, even though we are unholy. It’s the mystery of a holy God who cleanses his people from sin so that they can become holy too. And it’s the mystery of a holy God who wants his people to go into the world proclaiming his holiness to all who will listen. This month, we’re going to explore that holiness. First, we’ll look at how Scripture defines holiness. Then, in our second and third articles, we will hear Pope Francis reflect on what holiness looks like today.

The Lord Is Holy. The word “holy” comes from the Hebrew word qadosh, which means something cut off or set apart from everyday things. So when we say that God is holy, we are saying that he is separate from, other than, us. He is so high above us in his perfection and power and glory that he deserves to be honored above all other things.

We don’t often think about the holiness of God, and when we do, it can make us nervous. It might be easier to think about holy people like the saints. But God’s holiness is infinitely greater than the holiest of saints. His holiness is beyond our highest standards because he is the standard.

Throughout the Old Testament, God revealed himself as holy. When he spoke to Moses from the burning bush, he commanded him to remove his shoes because even the ground around him was holy (Exodus 3:5). The people of Israel were forbidden to touch the mountain where God appeared because of his holiness (19:21). And when God revealed himself on Mount Sinai, his holiness made Moses’ face shine so brightly that he had to wear a veil so as not to scare the people (34:29-30).

God’s love is holy—he wants only good for his people. His faithfulness is holy—he will never forsake his people. Even his judgment is holy—it expresses his desire to preserve, protect, and heal his people. He cannot abide anything that degrades or destroys his people whom he created. And yet as holy and “other” as he is, God decided to come and walk among us as a man. Jesus, “the image of the invisible God,” became one like us so that he could manifest God’s holiness and show us the way to become holy ourselves (Colossians 1:15).

Jesus Is Holy. Jesus’ holiness is unique. While God’s presence made the mountain holy and made Moses’ face shine, Jesus is holy within himself. He does not only reflect God’s holiness, he is holy—the Holy One of God.

Many people did not recognize Jesus’ holiness, but some did. John the Baptist protested that Jesus should baptize him because he knew he wasn’t worthy even to untie Jesus’ sandals, let alone baptize him (Matthew 3:11, 14; John 1:26-27). Even the unclean spirits could see his holiness. Terrified by his presence, they shrank from him and confessed him to be the “Holy One of God” (Luke 4:34).

Jesus manifested his holiness in everything he did. His miracles and healings, his teachings and acts of mercy, all revealed how much greater he is than us. At his transfiguration, the brightness of his majesty left Peter, James, and John speechless (Mark 9:1-9). And even when many disciples left him, those who remained did so because of his holiness: “We have come to believe and are convinced that you are the Holy One of God,” Peter proclaimed (John 6:69).

Those early believers who recognized Jesus’ holiness recognized something else as well: their sinfulness. When Peter witnessed Jesus’ miraculous catch of fish, “he fell at the knees of Jesus and said, ‘Depart from me, Lord, for I am a sinful man’” (Luke 5:8). And as happened with Isaiah, Jesus was not put off in the least by Peter’s sinfulness. Instead, he calmed Peter’s fears and called him to a life of “catching men” (5:10). Like Isaiah, Peter left everything and followed him.

Jesus showed his holiness most fully when he offered his life for us. “I consecrate myself for them,” he said on the night before he died (John 17:19). So great was his desire to make us holy that he held nothing back, not even his own life.

Jesus Makes Us Holy Today. From the time of Moses until today, God has called his people, all of us, to be holy. He made a covenant with us and set us apart because he wants his Church to become a blessing to the world around us. Just as his presence made Moses’ face shine, God’s presence among his people confers a genuine dignity and holiness on us.

In response, we need to embrace this call to be a holy people. We need to hear God say to us, “Be holy, for I, the Lord your God, am holy” (Leviticus 19:2). We may feel as if holiness is too hard to attain. And if you feel like that, you are right! But in Christ Jesus, God can make us holy. In fact, that’s exactly what Jesus came to do.

The Letter to the Hebrews tells us that Jesus’ death on the cross has the power to wash away our sins, to cleanse our consciences, and to make us holy (9:14, 26; 13:12). But we know that this doesn’t happen automatically. Through Baptism, we are indeed cleansed from original sin and Jesus’ holiness actually becomes our holiness (1 Corinthians 1:30). But it’s up to us to act in faith as we strive to live holy lives.

Made Holy in the Spirit. Jesus knows how hard this call to holiness can be. Sin is both attractive and powerful. That’s why he sent the Holy Spirit to live in us. Through the Spirit, we can find the power to say no to sin and say yes to God. Through the Spirit we can hear God’s voice and sense his presence. Best of all, through the Spirit we can know deep in our hearts that we are sons and daughters of God. Just think: you can have a closer relationship with God than even Moses or Isaiah did! You are his child. His holiness and his love dwell in you. That means you can always drink from the wellspring of his grace.

The first Christians can show us how we can cooperate with the Spirit and grow in holiness. They knew that they weren’t perfect. Like us, they had their flaws and weaknesses. But they were changed men and women. The Holy Spirit gave them a new identity and a new capacity for holiness. And so, day by day, they focused on becoming more and more “a royal priesthood, a holy nation, a people of his own” (1 Peter 2:9). And how did they do this? By committing themselves to “the teaching of the apostles and to the communal life, to the breaking of the bread and to the prayers” (Acts 2:42).

Even in the twenty-first century, our path remains much the same. We become holy by devoting time to God’s word, by encountering Jesus in the Eucharist, by seeking God’s presence in prayer, and by living the “communal life” of loving one another from the heart. In the next two articles, we’ll hear from Pope Francis what this might look like for our everyday lives.

May we never forget that we are a holy people who have been joined to a holy God. May we never forget that our destiny is to join the angels and saints in heaven in singing their unending hymn of praise: “Holy, holy, holy is the Lord!” (Revelation 4:8).