Faith on Earth? places a great deal of emphasis on obeying God’s law. Doesn’t the Apostle Paul say we are saved by grace and not by law?

Yes he does and we must agree with him. God, in His grace, sent His Son to die for us sinners and His sacrifice paid the penalty due us for our sin. We are saved by grace and not by law but salvation is the beginning, not the end of the Christian life.

The apostle doesn’t tell us we can go ahead and sin as we please. He tells us we must not sin. But to not sin is to obey God and to obey God is to obey His laws. Salvation is by God’s grace but sanctification is by God’s law.
1 John 3:4:  … sin is the transgression of the law.