These gestures are prescribed in the General Instruction of the Roman Missal, and accordingly should be practiced by all the faithful. Each of them also has a strong tradition in the celebration of Mass.
Concerning the making the sign of the cross at the proclamation of the Holy Gospel, after the deacon or priest says, “A reading from the Holy Gospel according to ….," he and the faithful make the sign of the cross with the thumb on the forehead, lips, and breast over the heart. (The deacon or priest also makes the sign of the cross on the Lectionary or Book of the Gospels.) The first recorded instance of making the sign of the cross at the proclamation of the gospel is found in the ninth century: Regimius of Auxerre (d. c. 908) in his Expositio recorded how the people in the congregation would sign their foreheads, and the deacon would sign his forehead and breast. By the eleventh century, as attested to by Pope Innocent III, the deacon would make the sign of the cross on the Lectionary or Book of Gospels, and then both he and the congregation would sign the forehead, lips, and breast. The significance of the threefold signing is that we want to hear the Holy Gospel with an open mind, proclaim it with our lips, and cherish and safeguard it in our hearts. We are imploring the Lord for the grace to receive, acknowledge, and then profess the faith that has been received in the Holy Gospel through our Lord, Jesus Christ, the Word of God incarnate.
During the Profession of Faith (the Nicene-Constantinopolitan Creed) all bow at the mystery of the incarnation: “…by the power of the Holy Spirit, He was born of the Virgin Mary and became man." Prior to the Novus Ordo of 1969, all genuflected at these words, and on the Solemnity of the Annunciation and on Christmas, we still do. The earliest record of this practice originates in the twelfth century, as found in the writings of Blessed Peter of Cluny (d. 1156), and in the rituals of the Carthusians and Premonstratensian orders. This physical gesture– whether bowing or genuflecting– makes us mindful of the ineffable mystery of the incarnation, when our Lord, Jesus Christ, entered this world for our salvation, true God becoming also true man.
Finally, the offering of a sign of peace (formally called the “Kiss of Peace") boasts an even greater tradition. St. Justin the Martyr (d. 165) in his First Apology (which provides one of the earliest written accounts of the Mass) described the offering of a sign of peace after the readings and introductory prayers, but before the offertory prayers. Tertullian (d. 250) regarded the Kiss of Peace as a “seal" placed upon the prayers offered. St. Cyril of Jerusalem (d. 386) in his Catechetical Lectures also recorded how the deacon would call for the congregation to exchange a sign of peace. Moreover, St. Cyril explained, “Do not suppose that this kiss is like those given by mutual friends in the marketplace. Such a kiss this is not. This kiss blends souls one with another, and woos for them forgetfulness of every injury. This kiss, then, is a sign of the intermingling of souls and of the banishment of every remembrance of injury. It was in this regard that Christ said, “If you are offering your gift at the altar, and while there you remember that your brother has something against, you, leave your gift at the altar and go out first and be reconciled to your brother; and then come up and offer your gift.’ The kiss, therefore is reconciliation, and because of this it is holy. Just so, where the blessed Paul cried out, saying, ‘Bid one another welcome in a holy kiss’ and Peter, ‘In a kiss of charity.’"
Seen as a natural prelude before the reception of Holy Communion and an affirmation of the whole meaning of the Mass, Pope Innocent I in a letter to the Bishop of Gubbio (416) mandated that the Kiss of Peace occur after the consecration. Later, Pope Gregory the Great (d. 604) set the exchange of the Kiss of Peace after the Our Father.
Because of the growth of the size of congregations over the centuries, how the Kiss of Peace was exchanged evolved. By the tenth century, the Kiss of Peace began at the altar and then emanated to the congregation. By the thirteen century a kissing board or “Pax board" (osculatorium) was introduced which the priest kissed and then this was passed through the congregation with each kissing it. Eventually, the sign of peace was offered only during the High Mass as an embrace between the priest, deacon, and subdeacon. In the low Mass the priest would simply kiss the altar, and say, “Pax tecum" followed by the response, “Et cum spiritu tuo."
In the Novus Ordo, the Kiss of Peace has been restored to its more traditional practice. The priest may invite the congregation to offer to each other a sign of peace “according to local custom." Note that the priest does not have to invite the congregation to do so; the verbal exchange between the priest and the congregation of “The peace of the Lord be with you always" followed by “And also with you" may suffice for this ritual. The actual sign of peace may include a handshake, embrace, or even a kiss for a loved one.
These gestures should be taken seriously and performed reverently. They are physical actions which help us form a proper spiritual disposition and reverence during the Holy Sacrifice of the Mass.