The simple answer is that God’s moral commandments are a reflection of God’s own character and thus are eternal, as Jesus Himself reiterated in the Sermon on the Mount: “For truly, I say to you, until heaven and earth pass away, not an iota, not a dot, will pass from the Law until all is accomplished.” (Matthew 5:18) So, the correct answer is “no.” God’s laws NEVER become obsolete.
But this simple answer might raise an objection: The Old Testament of the Bible is full of regulations that Christians consistently disregard! For example, the book of Leviticus contains detailed instructions about how to offer sacrifices, foods that cannot be eaten, and how to avoid and deal with ritual ‘impurity.’ So why do Christians think that such Biblical laws don’t apply to them? Well, that’s where things get more complicated!
First of all, we need to get our heads around the fact of God’s two covenants (or ‘testaments’). The first was with Abraham and his descendants by which the Jews were to be a special people through whom “shall all the nations of the earth be blessed.” (Genesis 22:18) To emphasize their special relationship with God, the Jews were given the many external signs and regulations which distinguished them from their heathen neighbors. In their everyday lives they were to be constantly set apart for God’s special purposes.
When Jesus came onto the scene as God’s long-promised Messiah through whom the older covenant would be fulfilled, He ushered in a new covenant which would apply to all humanity and would be lived through obedience of the heart rather than external signs and regulations. In the new covenant for humanity’s salvation, paid for in the blood of Christ (Luke 22:20) and sealed by His resurrection, it was apparent that God was doing something totally new in fulfillment of the many prophetic promises of the Old Testament (e.g., as foreshadowed in Jeremiah 31:31-34).
The earliest Christians, who were Jews, faced many questions about what this new relationship implied in terms of their covenantal laws, a topic directly or indirectly addressed by quite a lot of the New Testament writings. The book of Acts in particular describes how these questions were ultimately resolved.
Acts 10 tells the story of how the Apostle Peter was instructed through a dramatic vision that the restrictive “purity” laws so important to Jews were not to be an impediment to bringing the Gospel to the household of Cornelius, a Gentile, and how they too received the Holy Spirit. Acts 11:1-18 then tells how Peter related this new revelation to the Jerusalem church, by whom it was concluded that Gentiles were also to be included in the new covenant of salvation through Jesus the Messiah (Christ). Thus, the Apostle Paul began his missionary efforts to bring the Gospel to Gentiles. However, some Jewish Christians still insisted that male Gentile converts had to be circumcised – the required mark of obedience to the old covenant. Acts 15 then tells how a special meeting of the Christian leaders was convened in Jerusalem to determine God’s will for the people of His new covenant of salvation. The essential conclusion was that apart from idolatry and immorality, the Old Testament restrictions no longer applied.
Ever since, Christians have distinguished between the moral laws of the Old Testament (which Jesus in fact amplified in His Sermon on the Mount) and the ritual laws and restrictions which were the external signs of the older covenant. Now, it would be convenient if one could just point to specific chunks of the Old Testament as purely of the latter type — as for example those who have tried to characterize the entirety of Leviticus as only “purity rules.” However, that’s clearly not the case, as exemplified by Leviticus 19 which intersperses important moral precepts (e.g., verse 18: “love your neighbor as yourself”) with ritual distinctions (e.g., verse 27 pertaining to shaving). To help us sort this out, we Christians rely on the writings of the New Testament to clarify and reinforce the unchanging moral precepts still applicable to the people of the New Covenant. But the most important aspect of the New Covenant is that even our moral failings are fully forgiven by the sacrifice of Christ when we repent and trust in Him.