(condensed from Ein Ayah, Berachot 6:55)

Gemara: There are six things that are negative for a talmid chacham to do: … he should not talk to a woman in the marketplace … Rav Chisda says that this is so even if she is his wife.

Ein Ayah: It is extremely important to safeguard modest behavior, as it is protection from the damage that natural promiscuity can cause to the individual and the group. If one is not careful, modesty can wane from the hearts of people due to the impact of regularity. It is, therefore, proper to keep a distance between the genders and attach an element of embarrassment when people fail to do so. This stresses the important role that modesty has in completing a person as he strives for sanctity.

Embarrassment is always measured in comparison to the standards followed by the people of the highest standing, in our case, by scholars and people of good reputation. Although people of lower standing do not quite keep to that level, they can still maintain enough for the world to continue reasonably. For example, when important people wear particularly dignified clothes and act in a very distinguished manner, simpler people, while understanding that they are of a lower stature, will not allow themselves to sink to the lowest level either. From the top, a feeling trickles down that human beings must act differently than animals in their daily life. When the highest level people do not act with an extra level of dignity, matters will deteriorate by degree until simple people lose all semblance of self-dignity. With this come the dangers of people not holding back their inclinations due to embarrassment.

This is the reason that a Torah scholar should not speak even to his wife in the marketplace. It is not merely because some may not know that it is his wife, which is a matter of suspicion, but because intrinsically a scholar should demand a higher level of himself. He must go beyond the letter of the law to insure the strength of the moral structure of society as a whole.