The Eternal Father speaks to Catherine:

My Truth invited you to call out thus when He said: “Call and you will be answered; knock and it shall be opened to you; ask and it shall be given to you.” So I am telling you what I want you to do. Never relax your desire to ask for My help. Never lower you voice in crying out to Me to be merciful to the world. Never stop knocking at the door of my Truth by following in His footsteps. Find your delight with Him on the cross by feeding on souls for the glory and praise of My Name, and with restless heart bewail the death of the human race which you see reduced to such misery.
Through this lamentation and crying out it is My Will to be merciful to the world. This is what I require of My servants and this will be a sign to Me that you love Me in truth.

Taken from Dialogue of St Catherine,(Chapter 107), Translated by Suzanne Noffke, Classics of Western Spirituality Series.