The right shoulder - See Clarke on Exodus 29:27 (note).

And the right shoulder shall ye give unto the priest for an heave offering,.... Whether of an ox or a cow, a lamb or a goat:

of the sacrifices of your peace offerings; which were of either of these creatures; the Targum of Jonathan paraphrases it,"the right arm from the shoulder to the elbow.''The breast being the seat of wisdom, and the shoulder of strength, some think denote Christ as the wisdom and power of God unto his people, his priests, who have all their knowledge and strength from him, and who bears them on his heart and on his shoulder.

And the right shoulder shall ye give unto the priest for an heave offering of the sacrifices of your peace offerings.

7:28-34 The priest who offered, was to have the breast and the right shoulder. When the sacrifice was killed, the offerer himself must present God's part of it; that he might signify his cheerfully giving it up to God. He was with his own hands to lift it up, in token of his regard to God as the God of heaven; and then to wave it to and fro, in token of his regard to God as the Lord of the whole earth. Be persuaded and encouraged to feed and feast upon Christ, our Peace-offering. This blessed Peace-offering is not for the priests only, for saints of the highest rank and greatest eminence, but for the common people also. Take heed of delay. Many think to repent and return to God when they are dying and dropping into hell; but they should eat the peace-offering, and eat it now. Stay not till the day of the Lord's patience be run out, for eating the third day will not be accepted, nor will catching at Christ when thou art gone to hell!