We all enter adult life in the single state, but most do not spend their entire life in it. Most people will discern a calling to another pathway that they then commit their life to.
However, over time it may become apparent, either through circumstances as they emerge during life or via a calling that is detected, that to spend one's life in the single state is the best path - a means to live a life of value and purpose growing in love of God and being of service to His people.
In whichever way people find this path, it gives them a chance to commit to looking at the gifts they have and how they can use them and the opportunities that come with living as a single person to act in service to society as fully as they can.
Single life is also likely to grant them the time to better develop a spiritual life so that they can come to know the love and care of God in their life.
In considering the vocation to the single life, you may find the following reading of use:
‘Single for a Greater Purpose - A Hidden Joy in the Catholic Church’, by Luanne Zurlo
‘Single and Catholic’, by Judy Keane