The Apostle Paul in the Book of Acts spoke about “becoming like one of them” in order to witness to the pagan world around him. He did not mean to blend into the society, to be like one of them, to do what they do; so he could have an opportunity to witness to them.
If Paul acted like them he would not have stood out from among them. “Becoming like one of them”, means to understand what they believe and why they believe it so you can witness to them intelligently and show them the errors of their belief system, the flaws contained within their worldview.
Therefore, you and I are to be salt and light in a Godless society. We are to open our mouths whenever the Holy Spirit gives us an opportunity to witness to a forever dying soul. We are never to compromise our life, our walk or our talk. All three must be unified for us to effectively witness to non-believers.