Bhagavad Gita Verse 63, Chapter 18

iti te jnaanamaakhyaatam guhyaadruhyaataram mayaa |
vimrishyaitadasheshena yathechhasi tathaa kuru || 63 ||
 
In this manner, I have declared that knowledge to you which is most secret among all secrets. Reflect on this fully, then do as you desire.
 
iti : in this manner
te : to you
jnaanam : knowledge
aakhyaatam : declared
guhyaat : of the secret
guhyaataram : most secret
mayaa : I have
vimrishya : reflect
etat : this
asheshena : fully
yatha : what
ichhasi : desire
tathaa : that
kuru : do
 
We have come across the word "iti" several times in the Gita discourse. It is always used to conclude a chapter, and also to conclude a major theme or topic. Here, Shri Krishna uses this word to inform Arjuna that the Gita discourse has concluded with this shloka. We have to note that the Gita is but one portion of the Mahaabhaarata epic. So the shlokas that follow this one are used to summarize the main teaching, and to link back to the conversation between Sanjaya and Dhritarashtra.
 
Shri Krishna also emphasizes the most secret aspect of this text. We have to understand the implication of the word secret here carefully. The Gita is by no means an exclusive text. There are several commentaries, including this one, that are freely available on the web. Most people will not approach the Gita due to their preconceived notions. Some think it is outdated, some think it is impractical and so on. Only a few people are interested in the Gita, and of those, fewer still are willing to understand and change their approach to life based on it.
 
For any spiritual teaching to have an impact on our lives, it has to go through three steps. Shravana is actively listening to the text through a qualified teacher. Manana is reflection on the teaching, with a view to resolve all doubts or gaps in logic. Nidhidhyaasana is meditation and constant contemplation, with a view to assimilate that teaching completely. Many seekers are enthusiastic listeners, but they make the mistake of skipping the second step. In doing so, they are not able to see the value of the teaching in their own lives. Shri Krishna stresses the importance of reflection to Shri Krishna. He also gives Arjuna the freedom to apply the teaching based on this understanding born of out of reflection, instead of taking it at face value.