Qualified for the Work - D&C 4:5

... Faith, hope, charity and love, with an eye single to the glory of God, qualify him for the work.

 This passage is referring to the work of proclaiming the gospel. We see that faith is one of the requirements before we're qualified for the work.

In the Lectures on Faith, the Prophet Joseph points out that faith is a gift given to the righteous. It is when they have the "assurance that they were pursuing a course which was agreeable to the will of God", that they are secure in their exercise of faith. In other words, it is only when we are sure that the things we are doing are righteous that we have the confidence to act in faith.

Mormon Doctrine says: [Faith] is always given when righteousness is present, and the greater the measure of obedience to God's laws the greater will be the endowment of faith.

This falls in line with the topic scripture - the phrase "an eye single to the glory of God" means two things to me: 1) Purity of motive - we must have no objective other than the glory of God, otherwise our motives are misled and our faith is false. 2) Diligence - when our motives are right, and we have the assurance that our pursuits are in line with His will, an eye single to His glory means that our mind is that no other thing will derail us from that goal.

Now, supposing we have these attributes; are we now qualified to serve? As stated, apparently no other qualifications are necessary. If one has faith, it must be backed by personal righteousness. If one has hope, it must be in salvation through Jesus Christ. If one has charity and love, they must have selflessness and moral courage. And if one has an eye single to the glory of God, they must have pure motives. If these are not the qualifications to serve, I would ask what are?

Now, the qualification and the calling are two different things. But regardless of having a calling, we must be "anxiously engaged". But that is a topic for another day.