In Acts 18:18, Paul took a vow involving shaving his head and the only vow described in the Bible that involves shaving your head is the Nazarite vow in Numbers 6, which involves making sin offerings. Likewise, in Acts 21:20-24, Paul planned to pay for the offerings of others who had undertaken a similar vow in order to disprove false rumors that he was teaching against the law and in order to show that he continued to live in obedience to it. In Hebrews 8:4, it speaks about offerings that were still being made in accordance with the law, so offerings did not cease with the death and resurrection of Jesus, but only ceased because of the destruction of the 2nd temple, and if all of Israel has accepted Jesus as the Messiah, then the 2nd temple would not have been destroyed, and there would still be offerings being made. Laws in regard to temple practice that weren't followed after the destruction of the 1st temple were once again followed after the construction of the 2nd temple, so there is nothing about the destruction of the 2nd temple that means that those laws are no longer valid, or that they won't be followed after the construction of the 3rd temple (Ezekiel 44-46). All of Scripture testifies about Christ (John 5:39-40), so we should live in a way that testifies about him by faithfully living in accordance with it as far as we are able.