Mar 3:4 Is it lawful to do good on the sabbath days, or to do evil? to save life, or to kill?
Alternative: Is it allowed to do good on the Sabbath or to injure? to keep a soul alive or to slay?

Here, Christ uses the words that mean "good" and "evil" in Greek, which is rare. The terms normally translated as "good" and "evil" are more accurately translated as "beautiful" and "worthless." (More on this topic here.) In this case, Christ is clearly referring to morale ideas and their relationship to religious teaching.

The question about the Sabbath could be applied to any religious restriction. The issue here is purpose: what is the purpose of religion? Christ asks very simply whether or not the ultimate purpose is to do good or to do evil, and, to clarify how he defines "good" and "evil," he goes on to specific saving life or taking life.

This question obviously lies at the heart of all religious questions. Christ has said that the Sabbath, and by extension religion, exists for humanity. Religion is a servant not a master. Any faith that seeks to make religion a master is contrary to Christ's teaching.

By Christ's logic, the purpose of religion is to preserve life, that is, do good. Religion can and does save lives by teaching ways to life that preserve life. By extension, we can never justify taking a life on religous grounds. The only reason for taking a life is to save other lives.

"Lawful" is exesti (exesti), which means "to be allowed," "is possible," and "to be in one's power."

"Do good" is from agathopoieô (agathopoieo), which means "to do good," "to do well," "to act rightly," and "to exert a beneficial influence."

"Do evil" is from kakopoieô (kakopoieo), which means "to do ill," "to play the knave," and "to do mischief," and "to injure."

"Save" is from sôizô (sozo), which means "save from death," "keep alive," "keep safe," "preserve," "maintain," "keep in mind," "carry off safely," and "rescue."

"Life" is from psuchê (psuche), which means "breath," "life," "self," "spirit," and "soul." It has the clear sense of the conscous self. It is also used to describe "the spirit" of things. It is often translated as "soul."

"Kill" is apokteinô (apokteino), which means "to kill," and "to slay" but it is a stronger form than the normal verb kteino. It is more like our "destroy."