Bhagavad Gita Verse 70, Chapter 2

aapuryamaanamachalapratishtham
samudraamaapah pravishanti yadvat |
tadvatkaamaa yam pravishanti sarve
sa shaantimaapnoti na kaamakaamee || 70 ||
 
Just like the ocean remains unmoved though water enters it from all sides, so does that (tranquil) individual attain peace in whom all desires enter, but not the "desirer of desires".
 
aapuryamaanam : filled with water from all sides
achalapratishtham : unmoved
samudram : ocean
aapah : water
pravishanti : enters
yadvat : just like
tadvat : so does
kaamaah : desires
yam : in that individual
pravishanti: enter
sah : that individual
shaantim : peace
aapnoti : attains
na : not
kaamakaamee : desirer of desires
 
Here Shri Krishna provides another pictorial description of the individual of steady wisdom : a deep, large ocean that has many streams of water entering it. No matter how many streams enter the ocean, regardless of how gently or how forcefully they enter it, the ocean always remains calm and undisturbed.
 
In the same way, an individual of steady wisdom does not get impacted by any number of material objects or desires that he experiences. They fail to disturb his state of equanimity. Furthermore, even if the individual has to get angry in order to perform his svadharma in the material world, he is rooted in tranquility. And that is just like the ocean surface could experience stormy weather, but remain tranquil underneath the surface.
 
On the other hand, the person who is steeped in ignorance and does not possess wisdom will never attain peace. Here he is called the "desirer of desires". In other words, this person still thinks that harbouring and fulfilling desires will lead to peace and happiness. The fundamental shift from selfish desire oriented work to svadharma prompted work has not happened for him.
 
Note the change in meter to emphasize the point made in this shloka.

Bhagavad Gita Verse 66, Chapter 2

naasti buddhiryuktasya na chaayuktasya bhaavana |
na chaabhaavayataha shaantirashaantasya kutaha sukham || 66 ||
 
The individual whose mind and senses are not controlled cannot have a focused intellect, without a focused intellect he cannot meditate, and without meditation there is no peace. How can there be happiness without peace?
 
na : not
asti : happen
buddhih : focused intellect
ayuktasya : one whose mind and senses are not controlled
na : not
cha : and
ayuktasya : that individual
bhaavana : meditation
na : not
cha : and
abhaavayataha : without meditation
shaantih : peace
ashaantasya : individual without peace
kutaha : where
sukham : happy
 
Shri Krishna so far extolled the virtues of controlling the senses and the mind. In this shloka, he echoes the same point, but uses negative inference to drive it home.
 
Here, he says that if the mind and senses constantly wander, our psyche is agitated. An agitated psyche will never allow an intellect to focus. And we have already seen in earlier shlokas the disadvantages of not having focused intellect or "vyavasaayaatmika buddhi".  One cannot hold on to a single thought, in other words - meditate, if the mind is turbulent.
 
We may feel that there is some repetition here - why is he asking us to control the mind and senses over and over again? But consider this: reading about it and putting it into practice are two different things. If we check the daily list of thoughts that we maintain in our diary, we realize that even if we read the Gita backwards and forwards, it takes lot of time and effort to change the quality and quantity of our thoughts. This message needs to be seared into our brain for us to take it seriously, hence the refrain of this point.
 
Very simply put: there is no happiness without control of mind and senses.