Romans 1:16-25 / Luke 11:37-41
It can be rather difficult to explain why some people believe in God and yet there are also others who don't.
As for those who don't believe in God, the 1st reading tries to give an explanation.
It says bluntly that what can be known about God is perfectly plain since God Himself has made it plain.
Ever since God created the world, His everlasting power and glory, however invisible, have been there for the mind to see in the things He has made.
The problem is that the impiety and the depravity of men keep the truth of God imprisoned in their wickedness.
But that is not confined to just those do not believe in God. Even for those who say that they believe in God, they have to be aware of this "wickedness" in them.
As Jesus told the Pharisees in the gospel: You clean the outside of cup and plate, while inside yourselves you are filled with extortion and wickedness!
So even people who believe in God, even religious people, can succumb to the internal wickedness as those who don't believe in God.
But for us who believe in God, it is necessary for us to clean out this wickedness in us, and there is a solution.
As Jesus said in the gospel: Give alms from what you have and then indeed everything will be clean for you.
So if we say we believe in God, then the proof of it is that we will give alms and serve the poor.
Not only will it cleanse our hearts, it will deepen our faith in God who cares for the weak and the poor and helpless.