Suffer and endure…

Dear souls that seek to walk in security and comfort in spiritual things: If you knew just how necessary it is to suffer and to endure in order to reach such a lofty state of security and consolation… then you would in no way seek consolation, either from God or from creatures, but would rather bear the cross and, having embraced it, would desire to drink pure vinegar and gall, and would count this a great happiness.
–Saint John of the Cross (1542-1591)

Fortitude and perseverance…

And although many conflicts of diverse kinds should abound in prayer, and darkness of mind with much confusion, the devil making the soul feel that her prayer was not pleasing to God, nevertheless, she ought not to give up on account of those conflicts and shadows, but to abide firm in fortitude and long perseverance, considering that the devil so does to draw her away from prayer the mother, and God permits it to test the fortitude and constancy of that soul.
–Saint Catherine of Siena  (1347-1380)

Persevering until death…

Above all, as sanctity does not consist in being faithful for a day or a year but in persevering until death, we must use God as a shield which covers us completely because we are attacked from all sides. God must do everything. All the better; there will be no fear of failure. As for ourselves, we have only to acknowledge our power­lessness and to be fervent and constant in asking for help through the intercession of Mary, to whom God refuses nothing.
–Saint Claude de la Colombiere (1641-1682)

In prayer, never let go…

In prayer one must hold fast and never let go, because the one who gives up loses all. If it seems that no one is listening to you, then cry out even louder. If you are driven out of one door, go back in by the other.
–Saint Jane Frances de Chantal (1572-1641)