A promise in Acts 16:31? In the book of Acts, chapter 16, verse 31, reads as follows:


  They replied, "Believe in the Lord Jesus and you will be saved, you and your household." (NET)
  They replied, "Believe in the Lord Jesus and you will be saved, along with everyone in your household." (NLT)


Some say that this verse is a promise. If a relative is saved, the whole family will also be in some future. How true is this?
It is clear that the verse cited, Acts 16:31, is a promise. The question is, to whom does the promise apply? Taken in context, it is a promise to a particular individual in a specific instance. This verse is lifted from the narrative of Paul and Silas in jail in Phillipi, to which they had been delivered by the owners of a slave girl from whom they had driven an unclean spirit. In the narrative, there was an earthquake during which the doors of the jail came open, and the jailer was about to kill himself, believing that the prisoners had escaped. But Paul told the jailer that the prisoners were all accounted for, and in response to the jailer's question, "what must I do to be saved", Paul responds as quoted. The jailer took Paul to his house, and the jailer and his whole household were baptized. 

So yes, the statement of Paul is a promise, and contains, in my view, a bit of prophecy about immediately following events. The jailer believed, and the whole household was baptized. However, it is less clear that this a generalized promise to all mankind, that upon believing, the whole household of the believer will be saved. Were this true, it would put Paul against the prophet Micah, and Jesus, who taught about  intra-familial discord between sons and fathers, daughters and mothers, daughters-in-law and mothers-in-law, etc. (cf. Micah 7:6, Matthew 10:21, Matthew 12:34ff, and Luke 12:52-53).