What kind of person do you have to be in order to attend church?
If you were to ask most people what type of person God wanted to attend church, most would say a "good" person, meaning you have to be a good person before you can go to church in the first place. Even among those who could be persuaded that God wants bad people to go to church, would still make the excuse they have nothing to offer a bunch of good people.
The assumption is God only accepts people who are "good" or even "perfect" to serve Him.
This is the common way most people think about religion and attending church. Usually this is just an excuse and no amount of arguing will change a person's mind, but there are those who truly believe that God only wants good people to serve Him.
That should not surprise us, since the Jews of the first century held that same belief ... and Jesus condemned them for it. The Jewish converts to Christianity still had a problem worshipping with gentile believers. Paul had to write to address this issue, more than once, in his letters to them and even the apostle Peter had to be corrected in regards to his avoidance of gentile Christians.
Are you a dog? Have you ever thought of yourself in that way?
Too often we feel that we are not good enough for anything, so why would God want us to serve Him? It is the compassion God shows for us that proves His love for us.
He gave His Son for sinners, and so sinners are the only people He wants to serve Him.
If you don't think you are a sinner, God does not want you. If you think you are a dog who is only worthy of the crumbs from the Lord, then come right in! He's more than willing to give you a place.