Because Bhagavad Gita is spoken by the Supreme Personality of Godhead, one need not read any other Vedic literature. One need only attentively and regularly hear and read Bhagavad Gita.
Bhagavad Gita Introduction,
Those who have entered into a transcendental relationship with Krishna relish at every step the descriptions of the pastimes of the Lord.
Bhagavad Gita 10.18,
Bhagavad-gita is the instruction given by Krishna, and Srimad-Bhagavatam is the book containing topics exclusively about Krishna and His devotees. These two books are the special nectar of the words of Krishna.
Srimad Bhagavatam 4.4.44,
Ignorance is the cause of sinful life, and sinful life is the cause of one’s dragging on in material existence.
Bhagavad Gita 4.31,
Intelligence refers to the power to analyze things in their proper perspective, and knowledge refers to understanding what is spirit and what is matter.
Bhagavad Gita 10.4,
Unless one reads the Bhagavad-gita in a submissive spirit, it is very difﬁcult to understand Bhagavad-gita, because it is a great mystery.