The word vocation comes from the Latin verb vocare, meaning to call. Hence, what Christians often consider to be their calling is also their vocation. Prior to the days of Luther, the Roman Catholic Church only considered a vocation to be within the church itself, a holy vocation, such as being a priest, nun, or monk. It was Luther who began applying the word vocation to even secular vocations. In his view, even "'secular' work [was] just as valuable in God's sight as 'religious' work" ("Lutheran Church of Australia"). According to Luther, "All Christians have a calling to serve others wherever they are placed in life"; hence, whether you are a nurse, a professor, a carpenter, or a clergymen, that profession is your calling and is your vocation ("Lutheran Church"). What's more, Luther related all vocations to the "masks of our Lord God," saying that He hides behind these masks as we do His works so that through us He can "do all things" (as cited in Veith, "The Doctrine of Vocation"). This concept of God doing all things is best expressed all throughout Psalms 147, such as in the passage:
He strengthens the bars of your gates
and blesses your people within you.
He grants peace to your borders
and satisfies you with the finest of wheat. (13-15, NIV)
Since this passage describes God as strengthening the "bars of your gates," the passage is actually indirectly describing God as either a blacksmith or a carpenter; hence, the passage is actually describing God as fixing the iron gates of the city, not through His own means, but through the vocations of His people, making this a perfect passage explaining exactly what vocations are and how God uses them. The same can be said of the verse describing His granting "peace" to the borders of the city, which can be likened to the military vocation, and the verse describing how He "satisfies" with "finest wheat," which can be likened to the vocation of farming or harvesting.