This may be some official “definition” of vocation, but it’s pretty tortured, and is the kind of thing that is just going to make people feel bad about being single. This is not productive thinking, I don’t care if it is coming officially from the Church.
There are plenty of “sacrifices” involved in living a single life, whether you voluntarily choose it or not. You do not have the benefits of a helpmate. You do not have a family. You are not permitted by the Church to have sex outside marriage, so you’re essentially choosing a lifetime of celibacy unless you commit sin. Many people who are single do not end up that way by choice, but rather by circumstance as marriage does not work out for them, and their lack of a marriage is a HUGE sacrifice - perhaps more so than the sacrifice of a person who is happily married and has to make some sacrifices for spouse and family, but in return gets the benefits of having a spouse and family.
Most people who get married nowadays are not approaching it with a big attitude of “I’m going to sacrifice my life for my spouse and family”. They are happy because they are in love and they have found a soul mate and helpmate; they are also happy because they are fulfilling societal expectations (marriage is usually viewed as an expectation or an achievement). One could argue that maybe they SHOULD focus more on the sacrificial aspect, and then there would be fewer divorces. But seems to me that it’s the single people who make the larger sacrifices in doing something that is more against the grain of societal expectations, might very well be more lonely, and gets judged as “not a vocation” (and judged in other ways) regardless of whether the person is out volunteering to help the poor eight days a week.
I stand by my original post. If someone wants to make a vocation out of their work, for example, that to me involves discernment (you choose a career), a public commitment (taking responsibility for the work that you put out, committing yourself to an employer or to building a business, not to mention that some professions such as doctor and lawyer DO Involve taking vows of some sort) and giving up some element of freedom to spend time on doing your job, improving your skills and helping/mentoring others in your work.
Regarding a vocation of just being single, I think some of the others on this thread like CajunJoy and Mrs. Cloisters have expressed some ways to go about that very well.
In short - a vocation is all about making a commitment to something and putting time and effort into it that you could be choosing to spend on something else. If you do not want to absolutely commit to staying single, because you’re not sure if you might find a spouse later, then you can commit to being the best, most moral and most helpful single person you can be while single.