The following is an excerpt from Craig Keener’s commentary on Acts. The comment comes from 20:37: “They all wept as they embraced him and kissed him.”
“Kissing normally expressed love; the term φιλέω, can mean either ‘love’ or ‘kiss,’ and occasionally writers played on words to signify both. In dramatic situations kissing and weeping were conjoined as here—for example, as signs of mourning the deceased or of the joy in being reunited. The imperfect tense may suggest repeated kissing, more emphatic than everyday greetings (although it should also be noted that Paul would have received repeated kisses even if each person kissed him only once).
Relatives greeted one another with kisses, notably when reunited or about to be separated. Kissing was a conventional greeting for family members. Thus, for example, Roman women kissed kinsmen; likewise, a child should kiss his mother and father. A mother’s kissing a son or a father’s kissing a daughter was normal, considered suspicious only if excessive and immodest. Male friends could embrace and kiss without sexual connotations; the kiss functioned as an intimate greeting. Kissing between friends was apparently less common in urban settings, however. Kisses could be conveyed by proxy, often in secondary greetings in letters.
Kisses further served as respectful greetings to one of higher status; they showed respect among social peers as well as connections between patrons and clients; one could also offer congratulatory kisses. Disciples and pupils kissed teachers; often on the head; in such cases, the kiss could be an affectionate contact on the mouth. One person who wished to honor his teacher in a particular extreme way kissed his feet. An arrogant person of wealth might offer his hand to be kissed. A general needing to secure soldiers’ favor might go about, greeting them with kisses. Kissing was such a standard salutation that neglecting it could function as an obvious insult.
A person might kiss another who pleased him; a kiss was generally seen as pleasant (Prov 24:26) and hence might function as a suitable reward. A king might rise to kiss a teacher whose wise discourse had pleased him (1 Esd 4:47). A rabbi might rise and kiss the head of a student who expounded well; a Roman patron could also greet a client with a kiss.
Kissing could also have sexual overtones, however, under some circumstances; demanding labial as well as genital virginity, a strict father executed his freedman for kissing the father’s daughter. Traditionally, Roman values condemned public erotic kissing, restricting it to the private sphere, but erotic banquets had given way to excesses.
Some kissing may have been on the cheek. Most kissing, however, was on the mouth (closer to, e.g., one older Russian form of greeting than to, e.g., the contemporary way of kissing cheeks in France or much of Latin America). This included kissing teachers, as noted above. One typically kissed relatives on the lips. Thus, for example, Roman women kissed kinsmen on the lips; mothers kissed daughters on the lips; a Roman father might kiss his son on the lips, albeit lightly, or his daughter on the lips in pure innocence. A mourning sister might wish to kiss her dead brother on the mouth; children might do likewise with a deceased mother. Facial kissing may have sometimes compromised hygiene; it was said that social kissing in Rome let to ‘at least one outbreak of an infectious disorder among the leading citizens.’
A kiss of greeting could become the occasion for lustful abuse, but such abuse could be betrayed by the kiss’s character. Kissing on the lips was common, but a kiss on the lips of a sister or mother was naturally said to be less passionate than that of a lover; likewise, maidens kissed one another on the lips, but only modestly. Thus a lustful deity in disguise might give himself away.
That Pauline (and other) Christians greeted with a kiss is clear in our early sources, where it appears less a rite than an expression of familiar affection. Later the ‘kiss of peace’ even achieved a liturgical role (Justin 1 Apol. 65). The earliest form of this practice probably was not limited to one’s own gender, producing condemnations for those who kissed a second time; concerned with abuses, Christians eventually restricted its practice to members of one’s own gender. It came to express Christian ideals of spiritual equality. Conjoined with embraces and weeping, the kisses here in Acts mean more than the casual kisses typically used to greet family, friends, or teacher; they resemble the stronger expressions of emotion encountered at sad partings (as here) or reunions.” (Acts Vol. 3, pp. 3071-73)
Keeners has over 40 footnotes in this section from both primary and secondary sources. Such a discussion is important for more than one reason not the least of which is cited in his footnote number 1265 “Given the pervasiveness of ancient kissing documented above (and the utter lack of initiatory significance in our NT texts), a writer’s association of early Christian kissing with Mysteries’ ‘rites of recognition’ (Mack, Lost Gospel, 220) unfortunately reflects the writer’s inadequate acquaintance with the range of sources.” (p. 3073)