The Pri Ha'aretz might help us understand the ramifications of this a little. In parashath Hayyei Sarah, he explains that Avraham finally reached a level where he was untouchable by the Yetzer Hara. This level bears a little explaining: No matter how high a level we achieved yesterday, when the Yetzer Hara gets the best of us today, we will fall, and all of our previous level will be given over to the klippoth. So basically, the more we achieve, the more we feed the other side! We can't win!
The only way around this, he explains, is through attaining levels of emunah, pure faith in HaShem, and yirah, awe of HaShem's greatness. As you replace your performance of the mitzwoth for personal gain with your performance of the mitzwoth out of emunah and yirah, you free your mitzwoth of any foothold the Yetzer Hara might have. Once you gain no personal benefit from your actions, then the Yetzer Hara can't either. In the end, once all of your middot are perfected in this manner and turned to causes other than yourself, you are free from the stranglehold of the Yetzer Hara.
From here we can see the dynamic nature of the system and how our intentions in performing the mitzwah affect us on an even deeper level than the performance of the mitzwah itself.
The power of our mitzwoth are beyond compare. Even the simplest of physical actions, when elevated through the performance of a mitzwah, clothes our soul in the lower Gan Eden, allowing us to receive directly from HaShem's infinite light. Because these actions are still vulnerable to the Yetzer Hara while we are still in this world--as long as we derive some intended benefit from their practice--they have as well a spiritual weakness, and that weakness makes them over-sensitive to the greater divine illumination of the higher Gan Eden.
At the level of the higher Gan Eden, only the purest intentions that were clothed in our mitzwoth can offer us the necessary interface to fully receive HaShem's boundless radiance. This is because they are completely impervious to the taint of the Yetzer Hara.
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