Paul has been setting the scene before he introduces the gospel (Romans 1:16-17).  The gospel means 'good news', so first he has to explain the 'bad news' to which the gospel is the antidote.  He says that the human heart is naturally opposed to God. That might be assumed for the Gentiles, but the Jews are no better. There is no saving power in religion.  Even the 'best' person is bad in God's sight.

Quoting from Psalm 14:2-3, Paul describes the extent of human hostility to God, leaving the Jews who knew the Psalm to fill in its first verse ... "The fool says in his heart, 'There is no God.' (Psalm 14:1). It is a sad fact that no religion (including the Jewish law) can remove the inevitable foolishness of mankind.  That foolishness for many people, even religious people, also removes their appetite to seek the true God who longs to reveal Himself to them (Jeremiah 29:13).  

There are many others who do seek God.  They may study religion and try to compose a God who can be appeased or pleased by good deeds.  But when Jesus Christ (Messiah) is presented, that foolishness cannot accept Him but replaces His grace by religious rules.  In trying to be worthy by themselves, they have become worthless.  In trying to be good they fail.  Putting it simply, nobody can be good enough to reach God the Father (Romans 2:5), which is why we need God the Son to come down to us, to be our Saviour (www.crosscheck.org.uk).

It is hard for moral, disciplined, respected, religious people to be told that they cannot please God by themselves: it is offensive to them to hear that they cannot avert the wrath of God by their pious worship or good deeds.  None of that can take sins away and make them 100% pure.  Sometimes it is easier for immoral people and criminals to repent because they cannot deny they are sinners – they were the people Jesus spent time with (Matthew 9:10-12).  The 'nice' people just think they need a bit more polish on their halo!  But they are so wrong.  So be gentle with your friends and colleagues, but also be firm, as you explain their need to repent and receive Jesus as Lord and Saviour (John 1:12).