The one true church is the universal body of believers everywhere who have given their hearts to Jesus Christ as Savior and Lord. That is the only true church (see Ephesians 1:22-23, Colossians 1:18).
The Bible teaches us that we must maintain the unity of the Spirit (see Ephesians 4:3) until we come into unity of faith (see Ephesians 4:13). In other words, spiritual unity is something that all Christians can have. Complete unity of knowledge is something for the future.
The fact that there are many different denominations reflects a lack of knowledge in the church. In many instances, it also reflects pride. People are unwilling to meet together with others and submit their concepts to the body of Christ. And many denominations have come about because of doctrinal error. What begins as a beautiful and fresh revelation of God often degenerates into lukewarmness and then into fighting what God is doing.
Many times those who claim to know God persecute those who really do. It becomes necessary for the Lord Himself to come back with a fresh revelation to break through the solidification of the orthodox believers. This happened in Israel. Israel had lost sight of the Lawgiver in their exaltation of the Law. They killed Jesus, who was the manifestation of God, in the name of their law.
In the Middle Ages, when the church had gained political as well as religious power, it began to grow corrupt. Then a reform movement came about through Martin Luther and others, who were persecuted severely by the church. Later on, Lutherans began to persecute Calvinists. Then Calvinists began to persecute Anabaptists, who brought out truth from God on baptism.
Still later, Baptists persecuted Pentecostals, who brought out a different truth about the baptism in the Holy Spirit. There have been succeeding waves of truth that God wants to restore to the church. These revelations of truth have been the seed for some of the major denominations, which many times began as despised and persecuted sects.
The new Christian needs to find a fellowship of believers who love the Lord and who believe the Bible. There are Episcopal priests who love God with all their hearts, who are filled with the Holy Spirit, who serve Jesus and whose churches are beautiful places of worship. In some Catholic churches, born-again Christians could feel at home. There are Baptist churches where members love God. Presbyterian churches where the members love God, as well as Methodist, Assemblies of God, Nazarene and Holiness churches and many others where the members love God.
When you are looking for a church home, the first thing to do is to ask the Lord to guide you. Ask Him where He wants you. Find a church that is true to the Bible, one where the people love Jesus Christ and serve Him as Lord. Are the doctrine, teaching and practice of that church in accordance with the Word of God? Do the members try to live out the doctrine they profess? If you find those characteristics and a warm fellowship, the church may be for you.