"God in His infinite goodness sometimes sees fit to test our courage and love by depriving us of the things which it seems to us would be advantageous to our souls; and if He finds us earnest in their pursuit, yet humble, tranquil and resigned to do without them if He wishes us to, He will give us more blessings than we should have had in possession of what we craved."St. Philip always sought to impart humility, an absolutely necessary virtue if we hope to receive any fruits from our faith. St. Philip is known as the "Humorous Saint," and his life further illustrates the close connection between humility and joy.
---St. Philip Neri
A few more quotes, via Catholic Fire and the all-knowing Wikipedia:
"A joyful heart is more easily made perfect than a downcast one."
"There is nothing which gives greater security to our actions, or more effectually cuts the snares the devil lays for us, than to follow another person’s will, rather than our own, in doing good."
“Bear the cross and do not make the cross bear you.”
“There is no purgatory in this world. Nothing but heaven or hell.”
“Sufferings are a kind of paradise to him who suffers them with patience, while they are a hell to him who has no patience.”
“The greatness of our love for God may be tested by the desire we have of suffering for His sake.”
"Cheerfulness strengthens the heart and makes us persevere in a good life. Therefore the servant of God ought always to be in good spirits."