Many people claim that the truth and God is in your heart, so you don’t need a guru or the vedas to find god and truth.
Sometimes they use Gītā 10.10 and 11 to substantiate this claim (which is ironic, since the claim itself would render Gītā no more important than a daydream your aunt had yesterday). However Gītā does not subscribe to this view, and this use of 10.10 and 11 is completely out-of-context and misleading.
To give the context, texts 10 and 11 do say that Krishna destroys our ignorance from the core of our hearts. But he has said many important things in the two texts before these statements. These four texts (8-11) are famous as a unit (“caturśloki gītā”) so they must be understood together.
Text 8 says we must first get the firm idea: “aham sarvasya prabhava” (consciousness is the source of everything and Krishna is the ultimate consciousness). Where will we get this idea? By a flash of insight? Maybe, but much more likely we will get it from the Vedas or something or someone influenced by the Veda.
Text 8 says this idea leads to “bhajan” (practice of devotion). How will we practice bhajan? We will figure it out on our own? OK, maybe, but much more likely we will be guided by someone who learned bhajan from the Goswāmī’s, who learned it from the Vedas.
Next, text 9 says: “kathā bodhaya paraspara” (they will comprehend my kathā amongst each other). Where does this kathā come from? Where do we get our information about Krishna? From our imagination? From our “heart”? Maybe to some extent, yes, but much more likely the vast majority of it comes, in seed form at least, from Śrīmad Bhāgavatam, if not some other purāṇa or Vedic upaniṣad.
ONLY THEN comes texts 10 and 11!
Text 10 says “dadāmi buddhi-yoga” (I give them the ability to directly comprehend me), as a reciprocation with “prīti-pūrvaka bhajan” (their bhakti practice becoming mature).
Text 11 says “ātma-bhāva-stha” (situated in the heart). But this primarily refers to “ajñāna-jaṁ tamas” (the darkness of ignorance). In other words it says that what we have at the core of our hearts is darkness, not truth. Secondarily, it refers to “ami” / “aham” (“I” / Krishna). This shows that Krishna enters the heart after giving the capacity to host him within our consciousness (buddhi-yoga), which in turn was given in reciprocation for our matured purification efforts (prīti-pūrva bhajan).
Once in the core of the heart, his presence immediately ignites the wick of consciousness with enlightenment (jñāna-dīpena-bhāsvata), which destroys the darkness that was previously occupying the core of the heart. So, our consciousness has the inherent capacity to be the container of truth and god, but it not initially so. Initially it is the container of darkness and a deluded self-concept.
This is why Gītā 15.15 says
sarvasya cāhaṁ hṛdi sanniviṣṭo
mattaḥ smṛtir jñānam apohanaṁ ca
vedaiś ca sarvair aham eva vedyo
vedānta-kṛd veda-vid eva cāham
“I permeate the core of everyone, and there grant accurate or inaccurate comprehension. I have created the Vedas, which, taken as a whole, are the source of accurate comprehension of me.”
This verse comes in the context of explaining how Krishna is the essence of everything that we are and everything that we experience. It explains why we are ignorant of that fact, and how we can become more aware of it. In it, Krishna says that he grants both the ignorance and the awareness, but he specifically says that he grants the awareness by providing the Vedas.
So, the idea that Krishna will enlighten us from our heart without the need of guru or śāstra is misleading. This doesn’t at all mean that we have to idolize everyone who pretends to be a guru, or any quote that claims to represent Vedic siddhānta. But it does mean that we need a real guru, who really understands and deeply realizes śāstra.