Why are all Christians anointed with holy oil Baptism in the New Covenant?
Because by Baptism, all Christians participate in the one priesthood in Christ.
"The anointing with sacred chrism signifies the gift of the Holy Spirit to the newly baptised, who has become a Christian, that is, one "anointed" by the Holy Spirit, incorporated into Christ, who is appointed priest, prophet, and king." (CCC 1241 ) The ministerial priesthood is at the service of this common priesthood of all believers.
Because by Baptism, all Christians participate in the one priesthood in Christ.
"The anointing with sacred chrism signifies the gift of the Holy Spirit to the newly baptised, who has become a Christian, that is, one "anointed" by the Holy Spirit, incorporated into Christ, who is appointed priest, prophet, and king." (CCC 1241 ) The ministerial priesthood is at the service of this common priesthood of all believers.