To inquire of the Lord means to seek His guidance for direction on what to do in a particular situation. If we desire to be spiritually successful and not just earthly successful, we have inquire of god which is the best way to go.

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Judges 18:5-6 - "So they said to him, “Please inquire of God, that we may know whether the journey on which we go will be prosperous.” And the priest said to them, “Go in peace. The presence of the Lord be with you on your way.”