Acts 15 was concerned with the material things of Mosaic law such as circumcision, meats, washings . . . That law was abolished at the cross.
MUST we? No.
If that were the case then we are free to sin. Feel like some adultery? Indulge your self. See that new purse you've been longing for? Slip it under your coat. How much sin is too much for God?
The problem is that we humans are capable of obeying the letter of the law without having the heart for it
That doesn't sound like a defect in the Law to me.
If our focus is on law keeping, we’ve taken our eyes off Christ.
You make them sound incongruous. They are not. If we love Jesus we will love His Law. The Law is perfect. If you hate the Law you hate God. Matthew 5:48 states "Be ye therefore perfect, even as your Father which is in heaven is perfect." That doesn't sound like the Commandments are optional to me. How much sinning do you think is allowed in Heaven?
Just one...