"Mundaka Upanisad" compares the individual Soul and the Supersoul as two friendly birds sitting on the same tree (your body made of elements of nature). One of the birds who is the individual Soul, is eating the fruits of the tree (enjoying the pleasures of the senses afforded by the material body), while the other bird, the Supersoul (God) is simply watching his friend, the individual Soul. Of these two birds, although both are of the same quality, one is captivated by the fruits of the material tree (this material world) while the other is keeping watch on him only. Although they both are friends, one is the master and the other is the servant. Forgetfulness of this relationship by the individual Soul is the cause of one's changing his position from one tree to another, or moving from one body to another. The Jiva, or individual Soul, is struggling very hard on the tree of the material body, but as soon as it agrees to accept the other bird (God) as the Supreme spiritual master, (as Arjuna agrees to do so by voluntary surrender unto Lord Krishna for instructions), the subordinate bird immediately becomes free from all lamentations.
Below are verses from Mundaka Upanishad explaining that only:
"dva suparna sayuja sakhaya
samanam vriksham praishasvajate
tayor anyah pippalam svadv
atty anasnann anyo 'bhicakasiti"
In the tree of this body, Soul & Supersoul (God), are like two friendly birds sitting on the same tree. One of the birds (the individual atomic Soul) is eating the fruit of the tree (the sense gratification afforded by the material body), and the other bird (the Supersoul) is not trying to eat these fruits, but is simply watching His friend.
"samane vrikshe purusho nimagno
'nisaya socati muhyamanah jushtam
yada pasyati anyam isam asya
mahimanam iti vita-sokah"
Although the two birds are on the same tree, the eating bird is fully engrossed with anxiety and moroseness as the enjoyer of the fruits of the tree. But if in some way or other he turns his face to his friend who is the Lord, and knows His glories, at once the suffering bird becomes free of all anxieties.
Below are few verses from Bhagwat Gita which too explain about the nature of Soul & Supersoul:
"dvav imau purushau loke
ksharas chakshara eva cha
ksharah sarvani bhutani
kuta-stho ’kshara ucyate" (Bhagwat Gita: Chapter Fifteen verse 16)
"Sri Krishna said: O Arjuna, There are two classes of beings, the fallible (this body) and the infallible (this Soul). In the material world every living entity having a body is fallible, and while this Soul is infallible & it never dies.
"uttamah purushas tv anyah
yo loka-trayam avisya
bibharty avyaya ishvarah" (Bhagwat Gita: Chapter Fifteen verse 17)
"Sri Krishna said: O Arjuna, Besides these two (this body & this Soul), there is the greatest living personality, the God, the Supersoul, the imperishable Lord Himself, who has entered the three worlds and is maintaining them."
So now it is very clear, how this little individual Soul is different from the Supersoul (God) in nature. Though Soul is part & parcel of the Supersoul (God) only & both are unborn, imperishable but still one is limited in capacity & power, while the other is Lord of unlimited power. Individual Soul is the enjoyer of fruits of this vast nature, while Supersoul (God) is the provider of all these fruits & simply watches the actions & play of these different Souls. Let's turn our mind towards our friend Supersoul (God) who is sitting in our heart only in the subtle form. Doing so we shall come in His protection & He shall shower us with His divine love & grace always. So once we turn toward the God, we shall become free from all the anxieties & lamentations in life.