'Lawful' in the Bible

And certain of the Pharisees said unto them, Why do ye that which is not lawful to do on the sabbath days?

How he went into the house of God, and did take and eat the shewbread, and gave also to them that were with him; which it is not lawful to eat but for the priests alone?

Then said Jesus unto them, I will ask you one thing; Is it lawful on the sabbath days to do good, or to do evil? to save life, or to destroy it?

And Jesus answering spake unto the lawyers and Pharisees, saying, Is it lawful to heal on the sabbath day?

Is it lawful for us to give tribute unto Caesar, or no?