Notice the emphasis on the body. No gnosticism here!
When the bishop and the congregation have exchanged blessings, the bishop begins to give the Kiss of Peace, and the church herald, that is to say, the deacon, in a loud voice orders all the people to exchange the Kiss of Peace, following the bishop’s example. This kiss which all present exchange constitutes a kind of profession of the unity and charity that exists among them. Each of us gives the Kiss of Peace to the person next to us, and so in effect gives it to the whole assembly, because this act is an acknowledgement that we have all become the single body of Christ our Lord, and so must preserve with one another that harmony that exists among the limbs of a body, loving one another equally, supporting and helping one another, regarding the individual’s needs as concerns of the community, sympathizing with one another’s sorrows and sharing in one another’s joys.
The new birth that we underwent at baptism is unique for this reason, that it joins us into a natural unity; and so we all share the same food when we partake of the same body and the same blood, for we have been linked in the unity of baptism. St. Paul says: “Because there is one loaf, we who are many are one body, for we all partake of the same loaf. This is why before we approach the sacrament of the liturgy we are required to observe the custom of giving the Kiss of Peace, as a profession of unity and mutual charity. It would certainly not be right for those who form a single body, the body of the Church, to entertain hatred toward a brother or sister in the faith, who has shared the same birth so as to become a member of the same body, and whom we believe to be a member of Christ our Lord just as we are, and to share the same food at the spiritual table. Our Lord said: “Every one who is angry with his brother [or sister] without cause shall be liable to judgment.” This ceremony, then, is not only a profession of charity, but a reminder to us to lay aside all unholy enmity, if we feel that our cause of complaint against one of our brothers or sisters in the faith is not just. After our Lord had forbidden any unjust anger, he offered the following remedy to sinners of every kind: “If you are offering your gift at the altar, and there remember that your brother [or sister] has something against you, leave your gift there before the altar and go; first be reconciled to your brother [or sister], and then come and offer your gift.” He tells the sinner to seek immediately every means of reconciliation with the one offended, and not to presume to make an offering until amends are made to the one wronged and the sinner has done all that is possible to placate the offended person; for we all make the offering by the agency of the bishop.
Theodore, Bishop of Mopsuestia [d. 428], Baptismal Homily, 4.39-40