One must be careful not to mistake a necessary requirement for the sole requirement. Scripture discusses salvation many times and in varying ways; both directly and indirectly. One should look at all these verse to see common themes and what God intends for us rather than focusing on an interpretation of a single verse.
I would claim scripture knows nothing of a prayer that secures salvation followed by a life lived according to ones own rules. Salvation taking on a life of discipleship. An exchange of one life for another. Our sentence is death. We exchange our life for Christ's. He pays our debt and we live for him and not ourselves.
Jesus often talks of another kingdom. The kingdom of God or the kingdom of heaven. We become citizens of this kingdom but do so on Jesus' terms. This is the essence of repentance. Turning away from our sinful desires towards God's will.
There is a point in time when we turn from hiding our face from God to looking at him; from walking our own way to walking towards him. This "point of time" may be identified as "salvation" but the issue is that we persevere in the direction we have chosen.
No one can come to me unless the Father who sent me draws him. And I will raise him up on the last day. (Joh 6:44 ESV)So the Father has to draw us but we also have the ability to respond. Jesus said to the 12:
"Do you want to go away as well?" (Joh 6:67 ESV)Now our salvation is a work of God. There is no way we can be a part of God's kingdom by our own power. But when Jesus offers us to be part of his kingdom it is our freedom to accept or reject this offer. For those who have been taught this is a work, it is not; it is a response. Our turning to Jesus does not make us righteous, it is he who makes us righteous; but he will not do so unless we turn.
I think this is important because it is of eternal importance which kingdom we belong to. And it is extremely dangerous to think oneself saved when he is not! Jesus says:
"Not everyone who says to me, 'Lord, Lord,' will enter the kingdom of heaven, but the one who does the will of my Father who is in heaven. (Mat 7:21 ESV)It is possible that some of these know they never chose Christ, but it is also possible that some had thought they secured salvation according to what they had been (falsely) taught by man, but have never actually given their lives to him. If someone is not in the kingdom it is best he knows this in this age than think he is secure in a false salvation.