Romans 10:9

‘Because if you will confess with your mouth Jesus as Lord, and will believe in your heart that God raised him from the dead, you will be saved,”

What was required in order to be saved was confessing with the mouth Jesus as LORD, and believing in the heart that God had raised Him from the dead, (that is, had vindicated Him as the true Messiah, as the only One so raised). An open willingness to confess with the mouth what we believe about Jesus was thus seen as important. As Jesus had said to His disciples, ‘everyone therefore who will confess Me before men, him will I also confess you before My Father in Heaven' (Matthew 12:32). The main idea behind this was not so much witnessing, as being willing to take a stand when challenged. So to receive the righteousness which comes from faith it was necessary to take an open stand on the fact that Jesus is LORD (some see this as signifying a confession at adult baptism, but while that may be partly in mind it must not be limited to that. See Matthew 12:32; Philippians 2:11; 1 Corinthians 12:3), and to believe that God had vindicated Him and revealed the truth about Him through the resurrection, thereby demonstrating that He is the true and only Son of God (Romans 1:3). In other words receiving the righteousness that comes from faith requires belief in Who Jesus really is, ‘the Son of God with power', and belief in Him, and open acknowledgement of Him, as LORD.

The word ‘LORD' here has in mind the title of YHWH in the Old Testament. At some stage (although we do not know how early, for pre-Christian evidence for LXX is very limited) YHWH was almost always translated as ‘LORD (kurios)' in the LXX except when YHWH was linked with adonai (‘Lord'), and is so translated in many English versions (ASV is an exception). There is certainly evidence that prior to the time of Jesus the Jews were doing this orally. And it is quite clear from Old Testament citations in the New Testament that the early church did the same from the beginning (Acts 2:21; Acts 2:25). Thus the use of LORD (kurios) to signify YHWH is clearly attested. This is why Paul can constantly link God the Father with the LORD Jesus Christ on equal terms. He is thereby indicating their co-equality. Philippians 2:9 confirms this by informing us that, as a consequence of His resurrection, Jesus was declared to be LORD, which is the Name above every Name (i.e. the Name of YHWH), and had to be confessed as such, to the glory of God the Father, with people acknowledging Jesus as YHWH by bowing the knee and confessing Him as LORD (Philippians 2:10 with Isaiah 44:23). Compare also the equating of God with LORD in 1 Corinthians 8:6.