I am not sure where I first heard the expression "Ministry is inside-out not outside-in." I may have first heard it from Doug Kostowski who preached in Southern California years ago. I recall hearing him use this expression in a message.
I think the principle is very important though I am not sure I understood it fully for many years.
First, every Christian is an everyday minister. God uses each one of us for his purposes in some way. He gifts us and then empowers us with his Spirit for that ministry.
Second, everyday ministry is more than "church work." It is more than doing tasks. It is more than being on a committee or being involved in some project at "the building." Ministry is whatever we do which is used by God in some way to glorify him and serve another.
Third, ministry is a product of the "Spirituality" of a person. That is, the Spirit works within each one of us to create a Christ-like person (the Christ-formed person). Out of such a heart flows practical everyday ministry.
I like the way Norman Shawchuck and Roger Heuser describe "Spirituality."
Spirituality: The means by which we develop an awareness of the Spirit of God in us and the processes by which we keep that awareness alive and vital, to the end that we become formed in the Spirit of Christ.
(Shawchuck, Norman and Heuser, Roger, Leading the Congregation, p. 39)
Bottom line: Ministry must flow out of Spirituality. There, the Spirit is at work so that the ministry being done is not just a task being performed, but the Christ-formed life being expressed in practical ways.
Therein lies the secret of the easy yoke, according to Dallas Willard. In order to effectively follow Jesus in public ministry, we must also follow Jesus into the lonely desert and mountains to be alone with God. It is true that "a successful performance at a moment of crisis rests largely and essentially upon the depths of a self wisely and rigorously prepared in the totality of its being." In other words, "We who are appointed by God to heal others, need the physician ourselves. This necessary relationship between the leader’s private solitude and public ministry, according to Nouwen, can only be nourished "when we have met our Lord in the silent intimacy of our prayer" which will enable us also to "meet him in the camp, in the market, and in the town square. But when we have not met him in the center of our hearts, we cannot expect to meet him in he busyness of our daily lives."
(Shawchuck and Heuser, p. 42)