Christians that justify their decisions or actions by using a single sentence, phrase, or word from the Bible are often guilty of ignoring the essence of the message via intentional ignorance or a desire for misdirection to justify their actions. A closely related approach is when the reader interprets the importance of a Bible passage grossly out of proportion to the overall message as a justification.
By way of example consider the question, "Is killing wrong?" What about killing an assailant to protect another? Or, killing in war? What is the higher directive based on Jesus' example and the Bible's teaching—protecting others or avoiding murder at all costs? These are difficult questions that cannot be understood by reading a single sentence or passage.
It is harder—or at least requires more time spent in investigation, research, and thought—to understand the big message. Most worthwhile messages from the Bible cannot be understood from reading a single phrase but require reading many examples and extensive passages then engaging in thoughtful consideration. It is easy, and often a misinterpretation, to pick out a single phrase and claim to follow "Christian practice" by acting consistent with the one phrase rather than the entire body of teaching provided in the Bible. This notion is similar to the difference between an expert's views and a novice's (see: How is an expert's knowledge different from novice's).
Exodus 20
13 Thou shalt not kill.
Tho shalt not kill. But there's killing by Christians documented throughout the Bible. So is it okay to kill in some cases? If so, what are the cases? Is it a fixed knowable list or flexible and developed by the participant in real-time? Turns out, this is not a simple question resolved by one sentence. As with many such topics the deeper truth is only realized by deep thought informed by reading and study.
The New Testament also has passages that specifically speak to the issue of narrow interpretation. Given that "Christians" are attempting to live a "Christ like" life (after all it's in the name), then wouldn't the best guidance come from reading about Jesus' life in the New Testament of the Bible. So we go to the New Testament.
In Luke, we read Jesus' comments to the Pharisees as he accuses them of following the letter of the law (like following the specific phase or sentence in the Bible) but not the broader teaching that is the purpose of the law.
Luke 11 - King James Version
42 But woe unto you, Pharisees! for ye tithe mint and rue1 and all manner of herbs, and pass over judgment and the love of God: these ought ye to have done, and not to leave the other undone.
Luke 11 - New International Version (maybe a bit clearer to a 21st century human)
42 Woe to you Pharisees, because you give God a tenth of your mint, rue1 and all other kinds of garden herbs, but you neglect justice and the love of God. You should have practiced the latter without leaving the former undone.
Then in Mark, Jesus provides another example both in words and deed.
Mark
3:1: And he entered again into the synagogue; and there was a man there which had a withered hand.
3:2: And they watched him, whether he would heal him on the sabbath day; that they might accuse him2.
3:3: And he saith unto the man which had the withered hand, Stand forth.
3:4: And he saith unto them, Is it lawful to do good on the sabbath days, or to do evil? to save life, or to kill? But they held their peace.
3:5: And when he had looked round about on them with anger, being grieved for the hardness of their hearts, he saith unto the man, Stretch forth thine hand. And he stretched it out: and his hand was restored whole as the other.
3:6: And the Pharisees went forth, and straightway took counsel with the Herodians3 against him, how they might destroy him.
We see in the passage above that Jesus performs a healing on the sabbath where, by law, no such "work" is to be done on that day. Is the "no work" rule or law the important deciding factor or the general Christian principle that we should help others, and particularly the least among us? By his action, Jesus was demonstrating the answer.
If Jesus were to have only followed this "one phrase" rule that no work is to be done on the sabbath, then the man's hand would not have been healed and the higher calling never achieved.
Maybe modern day Christians can follow Jesus example. When narrow guidance gathered from the Bible is presented as absolute, pause and make sure that your actions are first and foremost consistent with the big ideas or teachings. Don't blindly follow a single sentence, maybe quoted by others, instead consider the big picture and Jesus teachings by example. Doing so might take a bit more mental work but it will result in far better outcomes for you and others.
1 Both mint and rue were valuable gifts at the time of Jesus. Mint is believed to be the oldest of the Mints (e.g., peppermint, spearmint, and cinnamon), for centuries used for its digestive benefits, often being served with or after meals to prevent or relieve gas, bloating, nausea and indigestion. Also used to soothe skin problems and headaches. Mint was widely used in Greece as an aphrodisiac. Rue, in ancient times it had the nickname “The Herb of Grace,” was an important culinary and medicinal herb. It is also mentioned in the Bible by its Greek name, “peganon.”↩
2 The accusation would be doing work on the sabbath, which was strictly prohibited.↩
3 The Herodians (Herodiani) were a sect of Hellenistic Jews mentioned in the New Testament on two occasions—first in Galilee, and later in Jerusalem—being hostile to Jesus. In each of these cases their name is coupled with that of the Pharisees.↩