The Scout Motto of the Scout Movement, in various languages, has been used by millions of Scouts around the world since 1907. Most of the member organisations of the World Association of Girl Guides and Girl Scouts (WAGGGS) share this same motto.

In English, this motto is most commonly Be Prepared, and it is no coincidence that this motto can be shortened to B. P. and Robert Baden-Powell, the founder of the movement, used to shorten his surname into B.-P.

In the third part of Scouting for Boys Robert Baden-Powell explains the meaning of the phrase:

The Scout Motto is: BE PREPARED which means you are always in a state of readiness in mind and body to do your DUTY.

Be Prepared in Mind by having disciplined yourself to be obedient to every order, and also by having thought out beforehand any accident or situation that might occur, so that you know the right thing to do at the right moment, and are willing to do it.
Be Prepared in Body by making yourself strong and active and able to do the right thing at the right moment, and do it.[1]
"To do the right thing at the right moment" can be extreme:

"Where a man has gone so far as to attempt suicide, a Scout should know what to do with him."[2]
"BE PREPARED to die for your country if need be, so that when the moment arrives you may charge home with confidence, not caring whether you are going to be killed or not"[3]
Also, the first handbook for Girl Guides, How Girls Can Help to Build Up the Empire by Agnes and Robert Baden-Powell, similarly explains:

The motto of the Girl Guides is "Be Prepared". Why is this? It is because, like the other Guides, you have to be prepared at any moment to face difficulties and even dangers by knowing what to do and how to do it.

Source en.wikipedia.org/wiki/Scou...repared.22