Vocational calling is something we tend to associate primarily with full-time pastoral ministry, and indeed, much of what the Bible says about God's call has to do with the call to ordained office. However, a brief survey of Scripture indicates that the Lord has always called people to vocations other than the pastorate or other offices in the church. Under the old covenant, for example, God called particular men to be kings of Israel. Exodus 35:30-35 explains how the Lord gifted Bezalel and Ohaliab with skills in architecture, metalworking, textiles, and so forth to help build the tabernacle. It's safe to assume that these men used these gifts to do other "nonreligious" jobs before and after the tabernacle was constructed.
When it comes to the gifts God has given, we find important teaching in Romans 12:1-8 on gifts in their relation to service in the church. Note how Paul indicates that not all Christians have the same gifts. Some are gifted to teach. Some have a particular aptitude for generosity. Others might be particularly gifted in serving the physical needs of their fellow believers. This list of gifts and graces is not exhaustive but representative, so there are many other ways that our Creator may gift His people. Moreover, as the Lord has always gifted people for service outside the church, we can make a secondary application to vocations that are not church offices. Just as God has not given the same spiritual gift to every believer, He has not granted the same skills and desires to everyone. No one is qualified for every job in the church, and no one is skilled to do every job in the world.
In light of that reality, Paul's admonition that we think of ourselves soberly makes a great deal of sense (v. 3). We are to think of ourselves appropriately, subjecting ourselves to critical self-examination so that we might discern our gifts and desires. In other words, we must subject ourselves to critical self-examination, asking ourselves where our talents and interests lie and being honest with ourselves about the answers. It is not humility to do absolutely everything we are asked to do. In fact, doing so can harm other people because we cannot do a good job when we are ill-equipped.
Critical self-examination is vital for discerning our vocation. If what we desire to do is permitted by Scripture, can contribute to the good of others, and is something we are able to do well, we can be confident that our desire matches God's calling.
It is a good for us to engage in critical self-assessment throughout our lives. Even if we have been in a particular job for a long time, the demands of the job and our interests can change to the point where we may no longer be a good fit for it. At that point, it may be time to consider another vocation. Self-assessment also helps us do our current work better. The more we know our gifts and desires, the better we can work with our coworkers to produce the best product or service possible.