God has decided to be our God. The Lord's faithfulness to our first parents even after they rebelled against his prohibition, and the crucifixion and resurrection of Jesus for the sin of the world proves it beyond a doubt. But, still, there's something that always causes us to doubt God's faithfulness.
We're born with doubt. Worse, we're born sinful. We're naturally selfish. We don't trust God's promise to be our gracious God, not even a bit. We prefer to do things our way, alone. We don't owe God anything. We didn't choose to be born. We definitely don't owe anyone else anything. That's our rebel heritage; what we inherited from our first parents. Our old self, the old sinner in us, doesn't like God or anyone else in control. We want to run things our way. That's why our old self will die. When we go it alone, without God or others, we will eventually get ourselves into a life or death situation where we can't rescue ourselves.
Our old self's favorite words are I, me, mine. Whether at home or work, we ask, "What's in it for me?" "How is this my problem?" "I just want what's mine." At church, our selfishness comes out as a confession of faith, "I know that God helps those who help themselves, and considering what I've done so far, how could God possibly ignore me?" Or, on the other hand, "I know God could never forgive me after what I've done."
Our old self's favorite words are I, me, mine.
That's how our old self tries to game the system. We make up the rules as we go, so they always benefit us, even if it means that we turn the world into a wasteland to win the game. We're so inherently selfish that we will play ourselves right out of the game into death.
The only reason we're aware of our old self is in baptism, God created a new self for us. It is the new version of ourselves that believes in God's promise to be our God and Father. We love all God has made, and we want to love and serve everyone and everything. The new version of us that's reborn in the waters of baptism lives and thrives on God's word of promise in Christ. Now, our new self wages a fight to the death with our old self. The old selfish sinner put to death so that our new self may live in and with Christ forever.
Thankfully, our God loves to create, redeem, and sanctify sinners. He lives to raise the dead and make them into a new creation. So he creates a new version of us in baptism. We may not look any different to the rest of the sinners around us, but to God, we've got a totally new look. Our new self fears, loves, and trusts God above all things. We live to play by God's rules. We don't game the system because that's the old sinner's thing. God pushed all his chips to the middle of the table and called the game.