Exodus 19.6
Septuagint

UmeiV de esesqe moi 
basileion ierateuma
kai 
eqnoV agiou
tauta ta rhmata ereiV toiV uioiV Israhl
 

New Testament - 1 Peter 2.9

umeiV de genoV eklekton, 
basileion ierateuma, 

eqnoV agion
laoV eiV peripoihsin, opwV taV aretaV ecaggeilhte tou ek skotouV umaV kalesantoV eiV to qaumaston autou fwV

Septuagint

 And ye shall be to me a royal priesthood and a holy nation:  these words shalt thou speak to the children of Israel

New Testament

But ye are an elect race, a royal priesthood, a holy nation, a people for God’s own possession, that ye may show forth the excellencies of him who called you out of darkness into his marvellous light shed abroad in all the earth

Masoretic Text

and ye shall be unto me a kingdom of priests, and a holy nation.  These are the words which thou shalt speak unto the children of Israel

Comments:  The MT has “kingdom of priests” in place of  “a royal priesthood.”