The first century Christians had no Bible to learn from. As they were a Jewish sect, they studied the Torah, Jewish Law, the prophets, and the psalms, especially all the scriptures they felt foreshadowed Jesus.
They made simple affirmations of faith, such as "Jesus is Lord." They had no real formal creeds or confessions and there was little structure to their worship. Their studies led to a shift from learning from the priests and rabbis for scriptural interpretation to Jesus and his followers, and the believe that the truth of the ancient texts could only be understood through the context of Jesus' ministry. The early Christians used allegory to imbue symbols and new interpretations from the older Jewish Scriptures. They beleived that the story of Sarah and Isaac symbolized the line of true believers, that Hagar and Ishmael stood for the Jews that rejected Christ. They also came to believe that by studying the ancient prophecies that the truth of the Lord could be revealed.
Even as the Jewish Sect of Christianity grew, it was spreading into the Hellenistic world. All the early non-Jewish converts were expected to convert to Judaism, until the Apostle Paul's teachings would change all that. Paul was a Hellenistic Jew who had been converted after a time of persecuting the Christians. He taught that it was more important to convert all mankind to Christianity, than to continuing the ordinances of Judaism. He was called to task for this and had to return to Jerusalem to answer to the early Christian leaders.
The main issue was whether these new converts had to be circumcised. According to the Book of Acts 15:1-21, there were some who taught that unless "you are circumciaed, according to the custom taught by Moses, you cannot be saved." Paul and Barnabus disputed this claim. The Christian Pharisees (yes, some of them had converted to Christianity), argued for circumcision and that all gentiles must be required to obey the law of Moses.
Paul stood and argued his case that, "God , who knows the heart, showed that he accepted them by giving the Holy Spirit to them, just as he did to us. he made no distinction between us and them, for he purified their hearts by faith." He went on to state that "We believe it is through the grace of our Lord Jesus that we are saved, just as they are." Paul won the arguement as James the Just (brother or cousin of Jesus, and current leader of the Christian Sect in Jerusalem), ruled that they should not make it difficult for the Gentiles who are "turning to God", but to council them in what is right.
In fact the idea of interpreting the Torah to understand Jesus can be seen in James the Just's ruling in Acts. "The words of the prophets are in agreement with this, as it is written: After this I will return and rebuild David's fallen tent. Its ruins I will rebuild, and I will restore it, that the remnant of men may seek the Lord, and all the Gentiles who bear my name, says the Lord, who does these things that have been known for ages."
Remember, we are saved by Grace, not by man, or by our own actions. Only by accepting the love of Christ, recognizing his sacrifice and resurrection, are we saved.
Peace and Love,