“and I will bring them.” When Christ conquers the earth and sets up his Millennial Kingdom, the scattered Israelites will all be gathered to the land of Israel again (see commentary on Jer. 32:37).
“in righteousness.” In this context, “righteousness” is doing what is right to God and others (see commentary on Matt. 5:6). It can be confusing to read that God will be Israel’s God “in faithfulness and in righteousness” because it seems that God has always been faithful and acted in righteousness to His people, and in fact He has. But in this fallen world in which the Devil is the god of the age (2 Cor. 4:4) and people have made many freewill decisions that go against God and His justice, God has not been free to execute His righteous acts. That will not be the case in the future when the Devil and demons will not be present and Christ will rule with a rod of iron.