A valid question. I’ll do my best to explain. In the book Acts of the Apostles is recorded the first council of the Christian Church…the Council of Jerusalem. This council came about as a result of dispute among the Apostles about the requirements for Gentiles wishing to become Christian. Mostly questions about whether or not Gentiles were required to adhere to the Law (which coincidentally, most of the Apostles and disciples were doing, being that they themselves were Jews). It was decided at that council that Jesus fulfilled the Law, and being the fulfillment, they were to live in the spirit of the Laws rather than the “letter”. Resultingly, alot of the perceived legalisms were done away with, and the Law was not regarded as the standard for living as it is defined in the Hebrew Scripture.
For example, it was no longer required to keep the Sabbath, but it was required that we attend church on Sunday and designate Sunday as a day of rest and reflection and devotion to God. Another example would be the Catholic Church’s view on divorce. The Law still applies to Christians, but since Christians believe the Law has been fulfilled through Christ, we live according to the spirit of the Law as we believe we were shown through Jesus.
Ultimately, as Catholics, we believe that the Church, guided by the Holy Spirit, has the authority to declare what is required of us, as Jesus handed the keys of the Kingdom to the Apostle Peter, giving Peter the power to “bind and loose” over the Church that Jesus established.