Prior to karate’s Japanification and move to a more sport oriented system, Okinawan karate (Tode, Te) was created for self-defense, or self-protection. One of Okinawa’s greatest fighters, Motobu Choki stated that; “Nothing is more harmful to the world than a martial art that is not effective in actual self-defense.”
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Today’s concept of blocking with one hand, then countering with the other hand (while always keeping the passive hand safely chambered at the hip) was not the original Okinawan way. This would have been a highly dangerous practice and would undoubtedly resulted in many serious injuries or possibly even death.
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Old-school, Okinawan Karate was grimy, dirty and raw. There was no room to stand in a fighting stance with your hands held high, or a zenkutsu dachi to wait for your deadly “one shot kill” counter punch. There was no safe distance several feet away from where to judge an enemy’s posture, size, strengths and weaknesses, or to ascertain if they were carrying a concealed weapon; before safely engaging him/her in a playful game of sparring or “kumite”.
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Motobu considered the use of “meotode”, in uchinaaguchi (the native Okinawan language) literally meaning “husband and wife hands”, as essential in his Karate. It was a way of maximizing strategical advantage in a physical altercation by utilizing both arms equally in continuously attacking and ‘blocking’ (receiving)….. “In the case of an actual fight both hands should always be used together.”
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In using meotode you never have a passive or active hand (what the old masters referred to as a “dead hand”). While we, today, are accustomed to always blocking with the front hand and counter striking with the back hand, this was certainly not the purpose in using meotode, as the front hand could actively switch between blocking and attacking in an instant, where the rear hand could jam, strike or grab at any time.
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“The blocking hand must be able to become the attacking hand in an instant. Blocking with one hand and then countering with the other is not true bujutsu. Real bujutsu presses forward and blocks and counters in the same motion.” – Motobu Choki
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Meotode is a concept, theory and principle, but also a technique…… No rules, no form, just pure efficiency. That, was the effective purpose of meotode. 
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References: With thanks to Jesse Enkamp. Note the term “blocking” is the modern translation which refers to “receiving”.
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