'Observance' in the Bible

As they traveled from town to town, they delivered the decrees decided on by the apostles and elders who were in Jerusalem, for the churches to observe.

Now they have been told about you, that you are teaching all the Jews who are living among the Gentiles to turn away from [the Law of] Moses, advising them not to circumcise their children or to live according to the [Mosaic] customs.

take these men and purify yourself along with them, and pay their expenses [for the temple offerings] so that they may shave their heads. Then everyone will know that there is nothing to the things they have been told about you, but that you yourself also follow and keep the Law.