Jews were required to wear the star of David so they know who were Jews or not and so they can't run and the Nazis know who they where
Answer 2
Strictly speaking, they weren't. The Star of David or Magen David is a symbol consisting of two superimposed triangular outlines. The yellow star that Jews have sometimes been required to wear as a distinguishing mark was a solid filled-in six-pointed star.
They were required to wear it so that other people would be reminded to ostracise and abuse them, to make them, and anyone who treated them decently, conspicuous.
There is no religious requirement to wear a Star of David, just as there is no requirement for Christians to wear a cross. However, in both cases, many people choose to do so simply as an expression of their faith.
If this is specifically asking about the Yellow Star that the Nazis required Jews to wear during Holocaust, the Jews wore this because it was national law to comply and non-compliance could mean harsh punishment, torture, and possibly death.
Answer
Jews were forced by the Nazis in Germany and occupied Europe to wear a yellow Star of David so that they could be instantly recognised as Jews. This was not the first time that Jews had been made to do this - they were subject to similar laws in most countries in Europe in the Middle Ages and in some places even longer.
Jews had to wear the Star of David because they were being singled out by the Nazis. It marked them out as the hated 'race'.
As for why Jews complied with the order, they did so because it was national law to comply and non-compliance could mean harsh punishment, torture, and possibly death.
Addendum
Strictly speaking, the yellow star that Jews have sometimes been required to wear is not a Star of David. The Star of David or Shield of David is not just any six-pointed star, it is a particular symbol consisting of two triangular outlines superimposed to make a star. Unlike the yellow star it is not filled in.
Jews were forced to wear Stars of David so that they could be readily and easily identified.
The purpose was to mark them out as Jews. It's much more effective than, say, dark hair. Not all European Jews were made to wear the Star of David - only those in Nazi-controlled countries.
As to be identified by the Nazis. Each Jew was to wear a band around their arm portraying the star of David.
The Star of David, or Magen David (Shield of David) as it's called in Hebrew, is worn by Jews as a symbol of the Jewish Nation.
they needed some kind of symbol to identify them, so a well known Jewish symbol was picked.
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The Jews were required to wear the Yellow Stars of David
The Star of David.
to identify them.
The Jews of Europe, during the holocaust.
The Jews were forced to wear that during the Holocaust.
Star of David
The Yellow Star of David .
striped pyjamus with a yellow star of david
by making it law.
No. The Star of David was yellow, not green. Additionally, they were not used in all Nazi-Occupied Regions, just most of them. (For example, in Denmark, Jews were not forced to wear the Star of David.) However, in countries like Germany, the Netherlands, and Poland, the Yellow Star was mandatory and the Jews were forced to wear them whenever they went into public.