Billy Graham popularised the notion that non-Christians had a God sized hole in their heart that needs filling. The idea was that non-believers were always looking for something - even though they did not know what it was - but that they felt empty without it. Graham suggested it was God that they were missing - so they should invite God into their heart to have this need satisfied.
Although I understand where he is coming from, I personally think it can be misleading. In the first place - our hearts don't just have a hole - they are broken and sinful. They need to be totally replaced, not just repaired. the bible says God will give a new heart - he calls this regeneration. Jesus called it being born again.
I also think it is not simply a matter of inviting Jesus into your heart. This implies that somehow we can do something - and that it is up to us to do the inviting. For me, this makes God rather pathetic. I think that when God moves - he moves and humans cant stop him. The example of Paul on the road to Damascus is a great example. Paul was intent on going to Damascus to put Christians into prison and possibly killed. Jesus confronted him on the road and essentially told him to stop resisting him. Paul was gobsmacked and immediately fell into line. Paul never invited Jesus into his heart - Jesus told him - and Paul cried out "yes Lord".
Regeneration is the activity of God. He changes our heart - and leads us to repentance over our sins - He declares us justified - and fills us with his Spirit. Jesus death on the cross is the legal justification for this declaration. His resurrection from the grave proves it. Pentecost - the outpouring of the Holy Spirit on the church - evidenced his ascension to heaven. In other words, if Jesus did not ascend to heaven, the Pentecost could not have occurred - and the church would not have been born.
The historical record - shows the exponential growth of the church was phenomenal. From a little over 12 disciples in or around 33 Ad to over half of the Roman kingdom some 300 years later - we are talking millions and millions of people - is staggering. And this was before Constantine declared the Roman nation Christian. In many ways the emperor had no choice - but to declare Rome Christian because Christians were everywhere and growing. He needed to legalise it - so he could control it.
Yet, despite the debates over whether Constantine's conversion were good or bad for the church - one thing is sure - the church had grown to such an extent - in such a short time even prior to Constantine - that if it was not the work of a divine hand which grew it, then what other possible - and indeed plausible explanation could there be other than the fact that Jesus died and rose from the grave.
This is one place where critics of the resurrection fall down. They pick on one thing - selectively but don't address the totality. The empty tomb. The eyewitnesses. The exponential growth of the church.
So Paul, my view would be get your bible out and start reading through the gospel of Mark. It is the shortest of the gospels and gets right into the ministry of Jesus fairly quickly. Reading the entire book in one sitting would be good - read it out loud too. when it was written it was written to be read out loud because most people could not read. And if you have any other questions - ask away.