Amri d'Bei Rabi Yani, kach amar Moshe lifnei Hakadosh Baruch Hu: Ribbono Shel Olam, bishvil kesef vzahav shehispata lahem l'Yisroel ad she'amru die hu garam lahem she'asu es ha'eigel - In the academy of Rabbi Yani they taught: so said Moshe Rabbeinu before HKB"H, "on account of the silver and gold you showered upon the Jewish people until they said 'enough', - this caused them to make the [golden] calf" (Berachos 32a).
Moshe Rabbeinu's attempt to mitigate the sin of the golden calf can be understood in [at least] two ways. First of all, affluence can generate a sense of complacency and self-centeredness. [Obviously, it need not generate such a result; but it definitely can do so.] Avodah zarah typically reduces religion to ritual, thereby relaxing if not outright eliminating the discipline which characterizes Torah. Hence, the attractiveness of the the eigel to people infected with smugness and self-centeredness. Smug self-centeredness and complete surrender to a religious moral code of behavior are simply antithetical. And indeed after worshiping the eigel, "vayakumu l'tzachek", they engaged in promiscuous behavior.
Moshe Rabbeinu's mitigation of Klal Yisroel's egregious offense may be understood on an additional level. Wealth can make a person materialistic. [Obviously it need not have that affect; but it definitely can.] The scourge of materialism not only distracts and diverts time and energy from Torah and mitzvos, but potentially also taints emunah. We believe in an infinite incorporeal Hashem. Hashem is unlimited and unbounded. The emphatically physical and materialistic mindset of materialism can lead one to a physical and materialistic religious mindset.
Many of the classical commentators explain that in making and worshiping the eigel hazahav the Jewish people were looking for some physical, tangible representation of HKB"H. This impulse, Moshe Rabbeinu argued in their defense, was strengthened by the riboy zahav, their drowning in gold and silver.
If we want to foster and cultivate pure emunah, we must avoid materialism. Materialism comes in different shapes and forms; it is not limited to the pursuit of pleasure or money. For instance, Careerism - defining and dedicating oneself to professional success as an end unto itself - is also a form of materialism. Any involvement with and focus upon the here-and-now / the physical as an end unto itself is a form of materialism.
The effects of materialism upon emunah will not always be as dramatic as is the idolatrous episode of the eigel. There are other more subtle and insidious consequences which result from insinuating the physical into the arena of faith. For instance, a materialistic mindset can influence us to understand anthropomorphisms literally. It can make it difficult for us to accept and yearn for the spirituality of olam haba. It can weaken our belief in the transcendent possibility of yeshuas Hashem k'heref ayin because of our pre-occupation with the physical and material which is limited and bounded, and so on. And thus we must avoid materialism in order to foster and cultivate pure emunah.