Bob Mumford, in Take Another Look at Guidance, compares discovering God's will with a sea captain's docking procedure:

A certain harbor in Italy can be reached only by sailing up a narrow channel between dangerous rocks and shoals. Over the years, many ships have been wrecked, and navigation is hazardous. To guide the ships safely into port, three lights have been mounted on three huge poles in the harbor. When the three lights are perfectly lined up and seen as one, the ship can safely proceed up the narrow channel. If the pilot sees two or three lights, he knows he's off course and in danger.

God has also provided three beacons to guide us. The same rules of navigation apply--the three lights must be lined up before it is safe for us to proceed. The three harbor lights of guidance are: 1. The Word of God (objective standard) 2. The Holy Spirit (subjective witness) 3. Circumstances (divine providence). Together they assure us that the directions we've received are from God and will lead us safely along his way.