If you go on a mission to preach the gospel with lightness...

If you go on a mission to preach the gospel with lightness and frivolity in your hearts, looking for this and that, and to learn what is in the world, and not having your minds riveted - yes, I may say riveted - on the cross of Christ, you will go and return in vain...Let your minds be centered on your missions, and labor earnestly to bring souls to Christ.