Tradition itself. The Church. Authority. Council. Commitment. Marriage. Becoming an acolyte.
The Hierophant is an interesting card in that it is greatly affected by the cards that are also in the spread. In this way it is much like pasta! If it is in a spread with many favorable romance cards, then it very often signals not only commitment, but a possibility of living together or even an engagement. This card paired with The Lovers, The Two of Cups, The Three of Cups, or any Knight or King (or Empress or Queen!) pumps up the juju on that being the likely future.
In the absence of these or a reading with many ill-favored cards, it can instead suggest the opposite: a desire to retreat a bit, focus on your traditional pursuits, and spend time with platonic friends.
It also can suggest a time of actual retreat! Going to meditate and drink cleansing juices for a week? This would be the card that suggests now is a good time for that and coming back renewed for a fresh start.
As an outcome card in a favorable spread, a happy commitment is definitely in the cards. In an unfavorable spread, this one might peter out simply because outside pressures of conformity, and possible religious incompatibility, are too great to overcome.