Do we think we are too bad?
Do we think we've messed up in our past too much?
Do we think that somehow His mercies are only available to certain people?
First of all, He sent His Son to take the punishment for sin for EVERYONE in the world. Not just a select few people. John 3: 16 says, "For God so love the world, that He gave His One and Only Son."
Then, if you look at many of who we call our "Bible Heroes of the Faith", they weren't perfect!
Abraham took matters into his own hands to have a child, when God clearly promised him one. He is still the "father of many nations" to this day.
Jacob stole his brother's blessing by pretending to be his twin. He is the "father of the 12 tribes".
Moses killed an Egyptian, but God used him to free the Israelites from slavery.
The key to remember is this.
God loves you. Period. No matter what!
NOTHING you can do will make Him love you any more, or any less.