When the Holy Spirit was come, He illumined the Apostles with truth, so that they saw the secret of the immeasurable love of the Word, with the will of the Father, who willed naught but our sanctification.

This has been shown us by the Blood of that sweet and enamoured Word, who was restored to His disciples, when the plenitude of the Holy Spirit came.

He came with the power of the Father, the wisdom of the Son, the mercy and clemency of the Holy Spirit, so the truth of Christ is fulfilled which He spake to His disciples: “I shall go and shall return to you”.

Then did He return, because the Holy Spirit could not come without the Son and the Father, because He was one thing with them.

Thus He came, as I said, with the power that is assigned to the Father, and the wisdom that is assigned to the Son, and the benevolence and love that is assigned to the Holy Spirit.

Well did the Apostles show it, for suddenly through love they lost their fear.

So in true wisdom they knew the truth, and went with great power against the infidels; they threw idols to the ground and drove out devils.

[…] As I have said, by remaining in fear alone, one would not escape hell; but would do like the thief, who does not steal, because he is afraid of the gallows; but he would not abstain from stealing if he did not expect to be punished.

It is just such a case when one loves God for the sweetness of it; that is, one would not be strong and perfect, but weak and imperfect

[…] The soul uplifts itself with deepest devotion, to love what God loves and to hate what He hates.

And it directs all its works in God, and does everything to the glory and praise of His Name.

This is the continual prayer of which Paul says “Pray without ceasing”.

Now this is the way to rise from being only a servant and a friend – that is, from servile fear and from tender love of one’s own consolation – and to arrive at being a true servant, true friend, true son.

For when one is truly made a son, he does not therefore lose being a servant and true friend; but is a servant and friend in truth, without any regard to himself, or to anything except pleasing God alone.

Catherine of Siena (1347-1380): Letter to Brother Matteo di Francesco Tolomei, OP.