Does it Matter What I believe? (Not finished)

The first question is this: does it even matter what you believe?
Yes it does, because there is little difference between what you believe and what you do,
and what you do really matters.
As long as you are alive, there is no such thing as being neutral. You are always choosing something. Sunday morning, if you believe that God would have you to go to church, you will get out of bed and get yourself there, and others will see this.
If you don't then you will have not been a blessing to others who went to church.

Some people say that Christianity is a licence to sin without any bad consequences, because Jesus paid the price for our sin, and so all you have to do is go back and forth between sinning and repenting and you can do whatever you want.

This is not what the Bible teaches, for several reasons.  Here is the first:

The word "repent" actually involves a change of mind.
This is part of the Greek word that is translated "repent" in the New Testament.
You can sin, and you surely can repent, but repentance really means that you want to not sin again.
If you keep doing this sin, then it is really questionable if you are really repenting.

Here is another: Christianity was never advertised as something you do on the side along with your sinning.

(story of John the Baptist here)
(story of rich young ruler here)
(story of Matthew's conversion here)

Here is the main reason you can't keep sinning as a Christian.  The new birth.