God leads you through the gifts God has given you.
"There are different kinds of gifts, but the same Spirit distributes them. There are different kinds of service, but the same Lord. There are different kinds of working, but in all of them and in everyone it is the same God at work" (1 Corinthians 12:4-6).
John Calvin tells us that that "all the gifts we possess have been bestowed by God and entrusted to us on condition that they be distributed for our neighbors' benefit" (Quoted in The Fabric of this World, p. 61).
A barrier to discerning your gifts: a deep sense of inadequacy.
A barrier to discerning the needs of the world: the size of the need.
