"When the Lord thy God shall cut off the nations from before thee, whither thou goest in to dispossess them, and thou dispossessest them, and dwellest in their land, take heed to thyself that thou be not ensnared to follow them after that they are desroyed from before thee, and that thou inquire not after their gods saying: 'How used these nations to serve their gods? Even so will I do likewise.' Thou shalt not do so to the Lord thy God for every abomination to the Lord which He hated have they done unto their gods, for even their sons and their daughters do they burn in the fire to their god." (Devarim 12:29-31)
Rashi and Ramban have very different approaches to this verse. Rashi's is generally straightforeward based on the pshat of the verse. Having conquered Eretz Yisrael, don't show up in the local towns and start worshipping the idols that the previous occupants used to.
Ramban has a difficulty with this. First of all, there are already plenty of references to the prohibition of avodah zarah in the Torah. Why does it need to be added in here? Secondly, the context makes no sense. Having just conquered the Land and vanquished its people along with their powerless idols, what sense would it make for our ancestors to want to start worshipping them? They'd just been shown to be unable to help their worshippers. What kind of useless religion is that?
Ramban then goes and looks at the juxtaposition of "How used these nations..." and "Thou shalt not do so" to derive a very different conclusion from Rashi. In his opinion, these verses are not speaking at all about our ancestors adopting the local idol worship customs of the Canaanites. Instead, they are cautioning against coming to an erroneous conclusion in a desire to worship God.
The concern was that our ancestors, after learning of how the locals used to worship their idols, might come to the conclusion that while worshipping the idol was wrong, the method used was not necessarily so. In other words, worshipping Merkulis (by throwing rocks at him) was wrong but throwing rocks in the worship of God might be acceptable! Thus they might start to use heathen methods in the Divine worship in addition to or instead of the already prescribed sacrificial ritual.
The implications from this understanding are important for Modern Orthodoxy. In contact with liberal secular society as it is, Modern Orthodoxy cannot help but be either overtly or subtly influenced by non-religious values. A result of this influence is a manifestation of the eternal Jewish curse: "let us be like all the other nations!" Whether in ritual, dress and thought, Modern Orthodoxy ascribes great value to secular culture and often tries to co-opt it into Judaism under the assumption that if frum Jews do it, they have taken something plain and added an element of holiness to it.
This has already removed what "authentic" Jewishness was left in Conservatism. Now Modern Orthodoxy seems hell-bent on following in its path. They have women priests, reverends and "rabbis", let's have maharats! They blur the religious distinction between men and women. Let's do the same! They place a higher premium on being politically correct and trendy than on observing tradition. Are we doing something like that? Never mind that there are deep reasons for the distinction between genders in Torah Judaism. What are the local nations doing? Let's be like them.
But according to the Ramban's understanding of the passage above, this is a huge mistake. What we know as Jewish traditional worship has not evolved as a matter of happenstance. The prayers in our siddurim weren't just whipped off by a bored sage a couple of thousand years ago. The piyutim aren't simply inspired poetry. Our routines and procedures aren't just rote performances devoid of inner meaning. To decide that whatever is liberally popular is acceptable for the shul betrays a complete lack of knowledge of this depth or its importance.
There are definitely areas of the outside world that Judaism can contribute to and benefit from. However, as the Ramban shows, how we worship is an area where we must remain distinct and loyal to our traditions, not our vapid neighbours.