Q: What is the duty which God requireth of man?
A: The duty which God requireth of man, is obedience to his revealed will.

Q: What did God at first reveal to man for the rule of his obedience?
A: The rule which God at first revealed to man for his obedience, was the moral law.

Q: Wherein is the moral law summarily comprehended?
A: The moral law is summarily comprehended in the ten commandments.

Q: What is the sum of the ten commandments?
A: The sum of the ten commandments is, To love the Lord our God with all our heart, with all our soul, with all our strength, and with all our mind; and our neighbour as ourselves.

(Questions XXXIX, XXXX, XXXXI and XXXXII from the Westminster Shorter Catechism)