Paul describes the Law as a guardian or supervisor (3:23-26, 4:1-3). This is a metaphor drawn from the well-known practice in the Greco-Roman world of assigning a slave to assist in raising one’s children, from six years into the late teen years. Typically a wealthy family would purchase a slave and assign him to the role of pedagogue, παιδαγωγός. This man would have been captured in war, perhaps a man who had some education, but was too old to work.
The guardian was not a teacher, although they may have assisted with learning. They were responsible for taking the child to his teacher and would keep him focused during his studies (sometimes with a stick!) The pedagogue was to be the moral guide for the child. Since a child was thought to be ruled by passions rather than by reason, the pedagogue was supposed to rule in those passions and teach the child how to live by reason. Plato describe the pedagogue as a horse’s bridle which restricted the natural passions of the child (See Plato, Laws, 808e).
Once a child “came of age,” there was no longer a need for the pedagogue, the child was “free” from their guardian. While a pedagogue may still be respected and honored, after the young man has reached maturity, the relationship ought to end.
In the literature of the Greco-Roman world, a pedagogue was sometimes characterized as rude, cantankerous, rough on their charges etc. Literature, however, does not always reflect reality. Think of how Victorian era British nannies are characterized in literature or film – sometimes they are witches, other times they are wonderful in every way. With respect to sexual morals, the pedagogue was a “strict kill-joy” (Young, 161).
But Paul is not emphasizing all aspects of a pedagogue. The nature of a metaphor is that some elements are highlighted, others are not. For example, that some literature describes the guardian as a slave-drive does not mean that Paul wants to describe the Law as a slave-driver. Nor does Paul want to communicate that the Law was a “kill-joy.” According to Romans 7 the Law is the perfect will of God, so it cannot be characterized as a wicked nanny.
The main point of the metaphor is that the role of the guardian is temporary. Once a child has reached maturity, the guardian no longer has any official authority of the child, and the child is foolish to continue to live under guardianship any longer. In fact, Paul will later describe the leading of the Spirit with a word related to a pedagogue. His point in this metaphor is that salvation history as moved on to a new age, from the Law to the Spirit. One is foolish to go back to the old guardianship of the Law once again.
Bibliography: Much of this material is drawn from Norman Young, “PAIDAGOGOS: The Social Setting of a Pauline Metaphor,” Novum Testamentum 29 (1987): 150-76. This is by far the best article on the pedagogue in the ancient world. Young’s more popular level article has illustrations of pedagogues from Greek art, “The Figure of Paidagogos in Art and Literature,” BA 53.2 (1990): 80-86. Witherington has an excursus on the Law as a Guardian in Galatians, 262-7, although he too is following Young.