'Is Double Predestination Biblical Or Not?' | R.C Sproul | Biblical Wisdom

Robert Charles Sproul was an American Reformed theologian and ordained pastor in the Presbyterian Church in America. He was the founder and chairman of Ligonier Ministries and could be heard daily on the Renewing Your Mind radio broadcast in the United States and internationally.Robert Charles Sproul was an American Reformed theologian and ordained pastor in the Presbyterian Church in America. He was the founder and chairman of Ligonier Ministries and could be heard daily on the Renewing Your Mind radio broadcast in the United States and internationally.

[evigrillo]

I want to understand this better; if God has already decided on the destination, then why do we share the gospel and pray for the lost?
Am asking just because I want to clarify myself and be able to better explain it to others.