A bit of piety amongst us Confessionals for the past several years has been to insist on calling the pastor's office his "study." The idea behind this piety is a good one: we're not office workers toiling away at "paper work," we are shepherd's who are called to study the Word of God in prayer.
So the piety is good, but the Latin is bad. Office comes from officium - duty. Your office is where you do your officia: and prayer and study are part of that. As are counseling folks in the Word of God, holding meetings with the elders, and the host of other things that take place in the office/study. These aren't the only officia of the Office, of course: you've also got an office before the altar, in the pulpit, by the bedside, in the classroom, at the font, and in the Confessional.
This is the geography of your ordination vows. Pull out the agenda and take a look. What are you supposed to be doing? What did you take a vow to do?
Lead a godly life
Diligently study the Scriptures and the Confessions
Be constant in prayer for those under your care
Preach and teach in accordance with the Confessions
Administer the Sacraments in accord with the Scriptures and the Confessions
Instruct young and old in the faith
Forgive the sins of the penitent and not divulge their sins
Minister to the sick and dying
Admonish and encourage the people to confidence in Christ and holy living
Those are the officia. Those tell you not only what to do, but where to be.
I originally looked at this pastoral geography as part of the Freed From the Shopkeeper's Prison set of presentations. There I point out what seems to us today to be a glaring omission in the vows: any mention of what we commonly call "evangelism." The vows don't place you on the front door step of a non-believer's home, or in a bar waiting to strike up a conversation with an atheist, or on a street corner handing out pamphlets. You are too busy for that: you've got other places to be.
The modern Arminian-influenced definition of evangelism has skewed our vision from the Biblical perspective. For Lutherans, "making a defense to anyone who asks you for a reason for the hope that is in you, doing it with gentleness and respect" (I Peter 3:15) is the key Biblical verse. In other words, where Arminians want to make a new category of Proselytizing Evangelism and place that in the uppermost of Christian duties, to which all other duties are subordinate, Lutherans just have Vocation. Do your officia where your officia place you and be ready to make a defense to anyone who asks you. The officia vocationis are the main thing, and the "making a defense to anyone who asks" is a byproduct.
And the pastoral vows bear this out. You are called to shepherd the flock. The Lord adds to the flock "when and where he pleases." Be ready to give a defense as you go about your officia - just like all other Christians do as they go about the officia of their vocations. Be where you are supposed to be, where you are vocatus to be, and do the officia you are supposed to be doing and "evangelism" takes care of itself.