'Observing' in the Bible

For [as I] was passing through and observing carefully your objects of worship, I even found an altar on which was inscribed, 'To an unknown God.' Therefore what you worship without knowing [it], this I proclaim to you--

Take these [men] [and] purify yourself along with them and {pay their expenses} so that they can shave [their] heads, and everyone will know that [the things] which they had been informed about you are nothing, but you yourself also agree with observing the law.