Contradiction with Hosea 1:9
This verse rejects the Israelites as God's people, while 1 Peter 2:10 affirms the believers as God's people, showing a reversal of status.
Hosea 1:9: Then said [God], Call his name Loammi: for ye [are] not my people, and I will not be your [God]. [Loammi: that is, Not my people]
Contradiction with Romans 9:25
Although this verse echoes the message in 1 Peter 2:10 by quoting Hosea to say those who were not God's people will become God's people, it shows the initial contradiction in status before God's mercy is applied.
Romans 9:25: As he saith also in Osee, I will call them my people, which were not my people; and her beloved, which was not beloved.
Contradiction with Deuteronomy 7:6
This verse emphasizes the Israelites as God's chosen people, in contrast to 1 Peter 2:10 which speaks of people who were once not considered as God's people.
Deuteronomy 7:6: For thou [art] an holy people unto the LORD thy God: the LORD thy God hath chosen thee to be a special people unto himself, above all people that [are] upon the face of the earth.