You have got to be a 'man of God', a man of interior life, a man of prayer and sacrifice. Your apostolate must be the overflow of your life 'within'. (The Way, 961)

Interior life. Sanctity in our ordinary tasks, sanctity in the little things we do, sanctity in our professional work, in our daily cares...; sanctity, so that we may sanctify others. A friend of mine was dreaming once. (He is someone I’ve never really managed to get to know!) He was flying very high, but he was not inside the plane, in the cabin. He was outside, on the wings. Poor soul, how he suffered! What anguish! It was as if Our Lord was showing him that just such insecurity and danger faces apostolic souls who would fly up to the heights of God, but have no interior life, or else neglect it. They are full of anxiety and doubt, and in constant danger of coming to grief.

I really do believe that a serious danger of losing the way threatens those who launch out into action — activism! — while neglecting prayer, self denial and those means without which it is impossible to achieve a solid piety: receiving the Sacraments frequently, meditation, examination of conscience, spiritual reading and constant recourse to Our Lady and the Guardian Angels... Besides, all these means contribute in a way that nothing else can, to making the Christian’s daily life a joyful one, for, from their hidden riches, flow out the sweetness and joy of God, like honey from the comb.

In our inner life, in our external behaviour, in our dealings with others, in our work, each of us must try to maintain a constant presence of God, conversing with him, carrying on a dialogue in a way that does not show outwardly. Or, rather, which as a rule does not express itself in audible words, but which certainly should show itself in the determination and loving care we put into carrying out all our duties, both great and small. (Friends of God, 18-19)

(http://www.opusdei.org.in/sec.php?s=310)