illustration (attribution, if any possible, is at the end of the article)
— HHDL Tenzin Gyatso
I think this quote should really be read "both ways":
• your 'enemy' is not an enemy at all, (s)he is your greatest friend or teacher; this is the classic reading and probably the intended meaning…
• your greatest friend or teacher actually is your enemy: this is less classic, but just as true in buddhist terms!
The reason your greatest friend or teacher is your enemy is because you may become complacent: you might stop looking, you might enter the "Gods' realms" where guidance is available, life is easy —or 'easier'— and where you delude yourself into thinking you've 'got' it, you've 'figured' it out!
Temporary absence of suffering might weaken the motivation to find how to cease suffering… But when dukkha arises again later, you will have wasted some time, possibly some extremely precious time (when you had many opportunities for clear thoughts, clear introspection, clear enquiry)!
A great teacher might be an excuse to become complacent because guidance seems always available, there appears to be less need to appropriate wisdom for yourself, it appears an "external solution" exists…
In the Mahāparinibbāna sutta (DN 16), it is said that the Buddha asserted that "the Tathāgata could, if he so desired, remain throughout a world-period or until the end of it" but, in his pain over the imminent death of the Buddha, Ānanda failed to pay attention to these suggestions and thus did not ask the Buddha to remain and keep teaching. When he finally requested so later, "the time [had] passed for such an entreaty."
Given how much the world could have benefitted from further spiritual guidance, one could question why the Buddha would need a formal request in order to remain! After all, he was a bodhisattva in earlier life and his understanding of inter-dependence and compassion is one of his forte.
The explanation from Mahāyāna Buddhism is that the Buddha wanted to impart a sense of urgency on us! That him staying for a whole world-period would have made us complacent, as there would then be no need to attain Nirvāṇa quickly if guidance was not fading but remained endlessly available, if we could always count on the perfect compassion of the Buddha… It is indeed compassionate to push us to provide the "right effort" to free ourselves, because the Buddha cannot liberate us, only we can: he can show the door, provide a raft, help remove barriers but we're the ones who have to cross the threshold, who have to cross to the other shore…
A great teacher might well be the strongest hindrance there is, your ultimate enemy, if you believe the solution to dissatisfaction is 'external' to you! Don't cling! Pay attention now! Learn now! Enquire now! Free yourself now!
photo: statue of Buddha (Jinju national museum, Korea)