The Catholic Church says it is the true Church of God
The church of God is the true church. It is not a denomination, neither does it belong to any single assembly. And membership comes through God and the revelation of Christ.
When Jesus taught about the kingdom, which the saints inherit, he spoke of the church and the offenses to come, exhorting and instructing us to be blameless, that we not cause offense (Matthew 18:15). He was speaking to his disciples - Christians.
He instructed us to seek peace, as when a brother trespass against another, to the extent of taking the matter to him and then to the church for them to judge. Which church was he speaking of?
The church at Jerusalem, at Antioch, Rome, Ephesus, Galatia...or the church in the house of Priscilla and Aquila, were all the church of God. None of them claimed to be the true church, or better, or more perfect in knowledge, etc., nevertheless they dealt with the same issues that cause divisions.
I think a church without spot or blemish is being built right before our eyes if we're in it, to the praise of God and not men.