Paul had a great burden for his fellow Israelites who were seeking God with zeal but completely missing Him (Ro.10:1,2). Not realising that they could never, however much they tried, manage to become good enough to be accepted by God, they were making the mistake of rejecting His free offer of salvation through Jesus the Christ (v.3). To receive acceptance as a free gift seemed to be foolish in their eyes because they felt that God could not accept anyone who wasn't good (1Co.1:18). When they felt that they were better than others around them they imagined that they would now be acceptable to God (Lk.18:11).
What do those who are born in 'Christian' families think many times? They know the true God, they are in the right religion, they have been baptised, they attend church and read the Bible, etc. They think God couldn't be so unrighteous as to reject them. The Gospel message is for all those in other religions, they think. Isn't this the worst deception of all, to imagine we have been accepted by God when we aren't, in truth? Jesus used the phrase 'twice as much a son of hell' – they are children of hell but they don't realise that because they imagine they are children of God (Mt.23:15)! That is a curse that many in the Christian religion are under!
Jesus said, to paraphrase, that He didn't come for those who thought of themselves as good people but those who realised they were sinners (Mk.2:17). To realise that we are sinners is the first step towards salvation. This happens when we come to see God as holy, righteous and just and how sin looks like in His eyes. When we hear about the judgment of God coming on every sinner – with or without a religious background – then we tremble before Him and realise that we have no hope at all because we are aware of many ways in which we have sinned before God. It is then, and only then, that we 'hear' the Gospel, that Jesus came to save us sinners, that there is free forgiveness available with God and that He will change our lives and help us to stop sinning (1Ti.1:15). We go to God asking for forgiveness and believing that Jesus has already taken the punishment that was due to us.
That is how we are born again, and without it, no one can enter the kingdom of God (Jn.3:3).
Jesus came to this world and died in order to save the ungodly (Ro.5:6). That was how God demonstrated before us not only His love but also His righteousness and justice (v.8). Sin had to be punished and there could be no free forgiveness that violated His justice. But Jesus took our punishment so that the love of God could be given freely to us.
We can receive this salvation only if go to Him and acknowledge that we don't deserve it and that we are helpless without it (vv.6,8). This is where nominal Christians fail: they can neither acknowledge that they are undeserving of the love of God nor that they are incapable and helpless when it comes to making themselves to be deserving.