What does Luke 3:6 mean?

John the Baptist began to preach shortly before Jesus started His public ministry. John called on people to repent of their sin (Luke 3:3). This fulfilled Old Testament prophecies which said a herald would precede the arrival of the Messiah (Malachi 3:1; 4:5–6). In this passage, Luke is quoting from Isaiah 40:3–5. The role of this "voice of one," calling out from the desert (Luke 1:80) is to prepare the people to meet their Savior. John's preaching ministry was very direct (Luke 3:7), and it was also clear. He did not claim to be the Promised One, instead indicating people should follow Jesus when He arrived (John 1:26–34; 3:30).

In this context, "the salvation of God" is a reference to the Messiah, the Promised One, who is Christ. The prediction is that all people will be made aware of this Savior (Romans 1:18–20), not that all people will be saved by Him (John 3:36). The gospel is universal in its availability: any who want to repent and express faith can be saved by doing so (John 6:37; 2 Peter 3:9). Not all will choose that path (John 3:18).