契約者=contractor よ=vocative case marker 我が=my (the archaic form of 私の) 盾=shield と=the case particle なり=ren'you-kei(連用形) form of the verb "なる/to become" 剣=sword と=the case particle なれ=the imperative form of the verb なる Contractor, Be my shield and sword.

Post duplicated.