How do baptized people share in the priesthood of Christ?

1 Peter 2:9 (KJV) - But ye are a chosen generation, a royal priesthood, an holy nation, a peculiar people; that ye should shew forth the praises of him who hath called you out of darkness into his marvellous light

All Christians have the responsibility of preserving and sharing the Gospel, and building our personal and communal (the Church) relationship with God.

This is to be differentiated from the ministerial priesthood. In both the Old Testament and New Testament, there are two priesthoods - universal priesthood of all believers, and the ministerial priesthood.

Exodus 19:6 (KJV) - And ye shall be unto me a kingdom of priests, and an holy nation. These are the words which thou shalt speak unto the children of Israel.

The two verses quoted here are about the universal priesthood.