You know… that to join two things together there must be nothing between them or there cannot be a perfect fusion.
Now realize that this is how God wants our soul to be, without any selfish love of ourselves or of others in between, just as God loves us without anything in between.

(From a letter by Saint Catherine of Siena, Doctor of the Church)

Catherine of Siena consecrated herself to Christ in a spiritual union from the age of 7. She joined the Dominican order, performing corporal works of mercy, counseling, and even convincing Pope Gregory XI to return to Rome, after a period when popes had retreated to Avignon, France.

We cannot think of this saintly doctor as meek and mild, as some try to think of Christ and His Gospel. From her letters to Pope Gregory XI:

“Be a manly man… wanting to live in peace is often the greatest cruelty. When the boil has come to a head it must be cut with the lance and burned with fire and if that is not done, and only a plaster is put on it the corruption will spread and that is often worse than death. I wish to see you as a manly man so that you may serve the Bride of Christ without fear, and work spiritually and temporally for the glory of God according to the needs of that sweet Bride in our times”

(quoted from this article)

Up, father! Put into effect the resolution you have made concerning your return. Why not give your life a thousand times, if necessary, for God’s honor and the salvation of His creatures? That is what He did, and you, His vicar, ought to be carrying on His work. It is to be expected that as long as you are His vicar you will follow your Lord’s way and example.

How do we achieve this zeal for following our Lord’s Way, for keeping His Word?

You are a mystery as deep as the sea; the more I search, the more I find, and the more I find the more I search for you. But I can never be satisfied; what I receive will ever leave me desiring more. When you fill my soul I have an even greater hunger, and I grow more famished for your light. I desire above all to see you, the true light, as you really are.

From the dialogue On Divine Providence by Saint Catherine of Siena, virgin and doctor of the Church