The Aron in the Mishkan was made out of wood, but it was covered on the inside and the outside with gold. Chazal (Yoma 72b) tell us that a true talmid chochom must resemble the Aron; his inside must exactly mirror his outside. From the writings of the Rambam we can glean how he explained this Gemara. He writes (Hil. Da'os 2, 6) "It is forbidden for one to smooth talk and cajole. He shall not say one thing with his mouth while intending something else in his heart; rather, his inside should be like his outside." A talmid chochom must say what he means and mean what he says.
Rav Wolbe writes (Alei Shur vol. II pg. 36) that it is interesting to note the importance that Chazal placed on this attribute. The Gemara (Brachos 28.) relates that Rabban Gamliel placed a guard at the door of the Beis Medrash and instructed him not to let in anybody whose outer conduct did not mirror their inner feelings. Even Rebbi Elazar ben Azaria, who subsequently removed the guard, did not disagree with Rabban Gamliel's restrictions; rather, he felt that everyone should be considered innocent until proven guilty. However, had he known for certain that a specific person did not meet this criteria he too would not have allowed such a student to enter the Beis Medrash.
We can deduce from here that the first step in becoming a talmid chochom is being meticulous with regard to one's speech. As the Rambam continues, "And even a single word of wheedling or deceit is forbidden - only true speech, an accurate spirit, and a pure heart devoid of any treachery and deception."
The two things that set humans apart from all other living creatures are intelligence and the ability to talk. This being the case, one must be sure to use this powerful tool of speech in the proper manner thereby manifesting that superiority. Moreover, the proper use of speech is a prerequisite to becoming a talmid chochom.