Dr. Ricks explains what this practice of clasping the right hands meant to the Romans:

In the Roman world, the right hand was sacred to Fides, the deity of fidelity. The clasping of the right hand was a solemn gesture of mutual fidelity and loyalty at the conclusion of an agreement or contract, the taking of an oath of allegiance, or reception in the mysteries, whose initiates were referred to as syndexioi (“joined by the right hand”).

Why is this practice so common among the early Christians? Dr. Ricks informs us:

They did so in part because they agreed with the non-Christian Romans that “fidelity and harmony are demanded in the longest-lasting and most intimate human relationship, marriage.” But they also did so because they accepted, perhaps, the ancient Israelite view that marriage was a sacred covenant and, further, because they understood “marriage,” in the words of the Protestant scholar Philip Schaff, “as a spiritual union of two souls for time and eternity.” A sacred handclasp-the dextrarum iunctio-was a fitting symbol for the most sacred act and moment in human life.

Dr. Ricks’ article is entitled “Dexiosis and Dextrarum Iunctio: The Sacred Handclasp in the Classical and Early Christian World.” Read the full study here. The PDF version contains several more illustrations of the dextrarum iunctio.

I have found additional material in conjunction with this practice that I will share in a future post.

Stephen Ricks On The Ancient Sacred Marital Handclasp