It may sound odd, but it seems to me that longevity in ministry has to do with whether pastors are adherent or inherent. Adherent is defined as “connected or associated with, esp. by contract.” Inherent is defined as “involved in the constitution or essential character of something.”* If pastors are adherent to the church, if they are externally attached, then short-term assignments are quite acceptable. If, on the other hand, pastors are inherent, if they are essential parts, then long-term assignments are fundamental to long-term growth. (definitions from the American Heritage Dictionary)
Biblical evidence seems to support the inherent pastorate. Ephesians 4:11-12 tells us that pastors (and others) are given by God to equip the saints until “we all attain the unity of faith.” In this chapter, Paul goes on to speak of the essential unity of the church. Further evidence of this essential unity is supplied by the various images of the church in the New Testament. The bride-groom, flock-shepherd, body-head, and branches-vine metaphors use corporate language to speak of the church as an essential unity. Only Christ is mentioned separately, and he is the essential foundation—THE inherent part, if you will.
If Christ himself is inherent to his body, then pastors are surely inherent members. Given that the church is expressed locally, pastors are then inherent parts of local assemblies. If it is true that pastors (regardless of the particular historical-cultural expression) arise naturally from the essential nature of the church, then they are not a mere structural necessity attached to the outside enabling the church to function. Rather, they are integral parts of the whole.