Titus 2:13-14, 1 Pt 2:9
In the Old Testament, God chose the Israelites and made them His people. (Deut 14:2)
Deut 14:2 For thou art an holy people unto the Lord thy God, and the Lord hath chosen thee to be a peculiar people unto himself, above all the nations that are upon the earth.
Because Jesus gave Himself for us, we became God's people. (Titus 2:13-14, 1 Pet 2:9)
Titus 2:13 Looking for that blessed hope, and the glorious appearing of the great God and our Saviour Jesus Christ; 14 Who gave himself for us, that he might redeem us from all iniquity, and purify unto himself a peculiar people, zealous of good works.
1 Pet 2:9 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;