If that dumb devil mentioned in the Gospel gets into your soul, he will spoil everything. On the other hand, if you get rid of him immediately, everything will turn out well; you will carry on merrily, and all will be well. Resolve firmly to be "savagely sincere'' in spiritual direction (always keeping your good manners) and to be sincere immediately. (The Forge, 127)
As I have already said, we all have our defects. But our defects should never be a reason for us to turn away from God’s Love. Rather should they lead us to cling to that Love, sheltering within his divine goodness, as the warriors of old did by climbing into their suits of armour. Our defence is the cry ecce ego, quia vocasti me, here I am, because you have called me. Just because we discover how fragile we are is no reason to run away from God. What we must do is to attack our defects, precisely because we know that God trusts us.
How shall we be able to overcome our meanness? Let me make the point again because it is so important: by being humble and by being sincere in spiritual direction and in the Sacrament of Penance. Go to those who direct your souls with your hearts open wide. Do not close your hearts, for if the dumb devil gets in, it is very difficult to get rid of him.
Forgive me for insisting on these points, but I believe it is absolutely necessary for you to have deeply impressed on your minds the fact that humility, together with its immediate consequence, sincerity; are the thread which links the other means together. These two virtues act as a foundation on which a solid victory can be built. If the dumb devil gets inside a soul, he ruins everything. On the other hand, if he is cast out immediately, everything turns out well; we are happy and life goes forward properly. Let us always be brutally sincere, but in a good mannered way.
I want one thing to be clear: I am not as worried about the heart or the flesh as I am about pride. Be humble. If ever you think you are completely and utterly right, you are not right at all. Go to spiritual direction with your soul wide open. Don’t close it because, I repeat, the dumb devil will get in, and it is difficult to get him out again.
Remember the poor boy who was possessed by a devil, and the disciples were unable to set him free. Only Our Lord could free him, by prayer and fasting. On that occasion the Master worked three miracles. The first enabled the boy to hear because, when the dumb devil gets control, the soul refuses to listen. The second made him speak, and the third expelled the devil. (Friends of God, 187-188)