God alone is Holy in and of himself. Holiness, perfection, love, etc are part of God by nature.
But no human is holy in and of themselves. Holiness is not part of human nature. We can become holy, but only insofar as we conform our will to God’s will, and that is exactly what Jesus Christ came to enable us to do.
Jesus looked at them and said, "For human beings this is impossible, but for God all things are possible." (Matthew 19:26)
Any holiness Mary, any of the saints, or anyone else has, is because of who they are in relation to God. Mary’s will is perfectly conformed to Gods’ will and Mary is without sin, so Mary is perfectly holy. Many saints were holy. Sometimes, at rare moments, you or I might even be holy. But we are not holy because of anything we oourselves possess, but rather because of God’s holiness in us.
I am the vine, you are the branches. Whoever remains in me and I in him will bear much fruit, because without me you can do nothing. (John 15:5)
God alone is holy - the source of holiness. Mary was holy, but only because she was perfectly conformed to God’s holiness. Without God, even Mary can do nothing. Eucharistic Prayer No. 3 says it perfectly:
Father, you are holy indeed, and all creation rightly gives you praise.
All life, all holiness comes from you through your Son,
Jesus Christ our Lord, by the working of the Holy Spirit.
We call the Pope the “Holy Father” while still recognizing that he is just an ordinary man. He is holy only because of who he is in relation to God.
-Tim-