“But as he which hath called you is holy, so be ye holy in all manner of conversation; Because it is written, Be ye holy; for I am holy” (1 Peter 1:15 - 16).
We are living in a day and age wherein what used to be expected as Christian behavior is now open to debate. This is something that never occurred in most of the 2,000 years since Calvary. There was no debate as to whether or not a Christian should live a pure, holy life. Instead, this was simply a given and assumed to be a basic truth that required absolutely no debate whatsoever.
In fact, if you were to go back and take a look at what all of the church's major denominations' requirements were, you'd probably be shocked to find that there were some really strict consequences to be faced by church members who lived lives that brought shame to the name of Christ Jesus. It was actually quite common to hear of members being barred from church membership for a certain period of time depending upon the nature of their offense. This is different from keeping them from attending church services. It simply meant that they had some of their membership's privileges suspended for a while.
Starting in the 1960s there was an air of rebellion that swept across America thanks to the hippie generation. Unfortunately, this began infecting the churches. At this time a teaching started developing that said that it was legalism to expect Christians to be held to certain behavior standards when it came to things like abstaining from alcohol, not smoking, being modest and not partaking of other such worldly vices.
Whenever you look up the real definition of the word legalism you'll find that it has to do with requiring works in order to be saved. There are a lot of religions that do teach this, including Islam. They teach that works are needed for salvation. Mormonism also believes that works are needed. In fact, whenever you talk to someone who belongs to the Mormon church they will tell you that both faith and works are needed in order for a person to be saved. This, in a nutshell, is legalism.
St. Peter plainly said that God commands us to be holy because He's holy. Does this mean that Peter was a legalist who wanted his views to be imposed upon other people too? Such a view doesn't make any sense whenever you consider that Peter walked side by side with Christ while he was on Earth.
God doesn't merely suggest that we be holy. Instead, He commands that we be holy. This holiness doesn't have anything to do with salvation either. The Bible plainly tells us that works (i.e. holy living) doesn't have anything to do with salvation. Of course, we are still called to live holy lives. Failure to do so means we don't love God, regardless of how much you may praise him because Jesus tells us that if we love Him, we're to keep His commandments. So, you can't love God but disobey His command to be holy.