So the preacher's advice to new missionaries was this:
1. Know our culture.
2. Bear with us because we are poor and not so much educated.
3. Learn our language, either Lubwisi or Lukonjo.
4. Know our beliefs, because sometimes we believe in these small gods.
5. Know what type of food we eat.
And his example was, that if you come to a home and find the kanumba (small shrine to ancestral spirits) out back, do not kick it down. Instead, sit and talk to the owner, and be patient, until he decides on his own to dismantle it. Excellent advice. It is always a danger to think we see the evil in another culture, and find too many things that fit the third category above. Instead we should look for more ways to honor the culture, to enter, to redeem, to strengthen its uniqueness. until the believers themselves sort out which aspects of their past were oppressive and wrong and should be left behind. God is merciful, both to us missionaries who have over-westernized too much of the world by painting in clear black and white strokes, and to indigenous Christians who cling to their views in tones of grey.
And lastly, it was a fascinating morning, because almost any other sermon I've heard on these Acts/Galatians type passages have interpreted them in light of a defense of salvation by grace (you don't have to be circumsized, or it's 20th century American religious equivalent of morality, to be saved) rather than as a defense of preserving old cultural ways (it's OK to keep circumsizing, to shave heads and pay vows, that Christianity is compatible with most aspects of cultural tradition).