What does Bhakti Yoga say about the nature of God in the Bhagavad Gita?

Bhagwad Gita has described several alternate ways or
practices for achieving the ultimate happiness or deliverance from the cycle of birth
and death. Each of this type of practice is named a different type of
yoga. Bhakti yoga, which means practice based
on devotion to the ultimate god, is one of these alternate practice. The details of
Bhakti yoga are covered primarily in the twelfth chapter of Gita.
However, this chapter describes the ways and characteristics of a devotee rather than
the nature of god. Thus Gita describes no particular view of God applicable exclusively
to Bhakti Yoga.

However, Gita does
describe he nature of ultimate god at many different places in many different ways. The
word limitation of eNoes, as well as complexity of the concepts, make it difficult for
me to give a comprehensive description of nature of God as per  Gita. However stated in
very simple words God has two different broad characteristics, which are apparently
mutually exclusive. Thus God is Described as formless (nirakar), At
the same time, God also takes on form as a sakar
incarnation.

The nirakar or formless
God is something that has no matter, occupies no space, has no form or any other
qualities - like colour, taste, mass and state - possessed by physical matters, has no
beginning and no end. It is interesting to note that having no beginning and no end,
makes the God of Geeta as something infinite, as well as  nothing. Thus Gita says that
when everything is eliminated, what remains is the God.

The
sakar God refers to incarnation of god in human or some other form.
The nirakar God takes on different sakar forms
from time to time for renovation or re-establishment
(sansthapanarthaya) of codes of good conduct
(dharma), for protection (paritranaya) of the
righteous people, and for elimination (vinashaya) of evil doers.
Bhakti Yoga generally is based on devotion to such sakar
God.