When Jesus died on the cross He was paying the price for redeeming the whole of mankind from the consequences and the power of sin (1Jn.2:1,2). But not everyone gets to enjoy this blessing except the ones who go to Him acknowledging their sins, repent from their sinful ways and put their trust in Jesus as their Saviour and Lord. Those who are unwilling to humble themselves in this way and receive this salvation as an unmerited gift may put up various excuses. But their loss is eternal, and the only reason is their own unwillingness to be honest with themselves.
But on the other hand, there seem to be a lot of people who assume they have been accepted by God for different reasons. They assume they are not as bad as those who deserve punishment, their good deeds outweigh their 'little mistakes', God is love and He will not punish them for their human weaknesses, they have done the best they could, God cannot ignore the sacrifices they have made for the church or poor people, they have been 'Christians' all their life, etc. The underlying assumption here is that they are 'good' and so God cannot reject them.
What is the deception that has caught all these people? That God can just wink His eyes over all the wrong things people have done if He finds them comparatively better than others. But that is something God is unable to do. He cannot gloss over sins; His righteousness demands that sin must be punished. That is why Jesus, the sinless Lamb of God had to die -- for our sins. But now that He has paid for sins, the offer is open for everyone.
But if we want to receive this free gift of salvation we must agree with the terms and conditions. We must agree that we deserve to be put to death for our sins and that we don't want to sin anymore. Then this offer of God will become available for us, but only then.
If we think in our heart that we are really good people, and that God ought to be delighted to have us with Him, we are seriously deceived. Jesus said, "It is not those who are healthy who need a physician, but those who are sick. I did not come to call the righteous, but sinners" (Mt.9:12,13). In other words, those who think they are good people cannot find acceptance from Jesus, but only those who sincerely recognise and acknowledge that they are sinners who deserve death.
Some are willing to say, "We are all sinners," "OK, I am the biggest sinner," loosely, without any conviction. They too won't enter the kingdom of God. Salvation is available on a personal basis, to all who go to God with true conviction of their sinfulness and who rejoice in the offer through the death of Jesus Christ. In principle this is very simple, but in practice very few are willing to take this humble position, and so very few finally get saved (Mt.7:14). If we don't want people to miss the true experience of salvation, we mustn't widen the narrow gate by watering down the doctrine of repentance or exaggerating that of grace.