ANSWER

According to the scriptures, a saint today is someone who has heard, believed and obeyed the gospel. The brethren in Philippi are said to be "saints."

"Paul and Timothy, bondservants of Jesus Christ, To all the saints in Christ Jesus who are in Philippi, with the bishops and deacons" (Phil. 1:1, NKJV)

Since they were in the "church," they believed and were baptized as per the case of the Phillippian Jailer.

"33 And he took them the same hour of the night and washed their stripes. And immediately he and all his family were baptized. 34 Now when he had brought them into his house, he set food before them; and he rejoiced, having believed in God with all his household" (Acts 16:33, 34)

The Jailer with his family "believed in God" when their faith acted and "were baptized." Then they were called "saints."