Does God Really Need a “Pound of Flesh” to Forgive Sins?

Questions about how to answer the challenge that God doesn’t need a “pound of flesh” to forgive sins but can simply forgive, and whether the claim in Romans 10:13 that everyone who calls on the name of the Lord will be saved contradicts Matthew 7:21.  

• How do you answer the challenge that God doesn’t need a “pound of flesh” to forgive sins but can simply forgive?
• Romans 10:13 says everyone who calls on the name of the Lord will be saved, but Matthew 7:21 says not everyone who says “Lord, Lord” will be saved. Can you help me understand this contradiction?