Jesus tells a simple story of two going to pray. One is in the religious elite, all smart and respectable. The other is a common person, with unsavoury behaviour to go with it. The two pray in quite different ways ...
The first says an eloquent prayer which is all about themself: starting with what they are not, and finishing with "look at me - I do this ...". The second stays at a distance, looks down, and just says it as it is: "I need mercy - my life is a wreck". Jesus remarks that it is the second person who went home justified before God. In a few short sentences we have another story where we can ask 'What does this tell us about God?', and 'what does it tell us about people?'.
Digging deeper this story gets at the important question 'How do we approach God?', and even 'How do I pray?'. Both of these are great questions - questions people who are enquiring or searching might ask. Talking with people suggests that they believe that they need to approach God in some special way, or use certain words, or that they are simply not worthy to do so. Jesus of course says do not be like the religious elite - cut the self-importance, instead come as you are right now. Of course recognise that God is mighty and we are just humans, with all the mess of our lives, but in that place we can still call on God.
It doesn't need special words - just honesty.
There is also a bigger deal going on. Luke places the story in a series (see chapter 18): the persistent widow, the Pharisee and the tax collector, the little children, the rich and the Kingdom of God. Let's hear that sequence again:
Widow, tax collector (sinner), little children ... can approach God and be embraced by Him.
Conversely the unjust judge, the religious elite, the puffed up and those clinging tightly to riches ... do not get that same treatment!
Jesus finished with a punchline: those who exalt themselves will be humbled, those who humble themselves will be exalted. This is the upside down nature of the Kingdom of God! It is a reverse to what we see in society.
Approach God, kind of like you are a small child. Don't make it too complicated. Remember that when sharing with enquiring friends, it doesn't have to be complicated. Start with the simple story, ask what it tells about God, what it shows about people ... and go from there. Draw conclusions by asking what does the story tell us we ought to do? And ask who they are going to tell?