Gita 04.03 explained
sa evāyaṁ mayā te ’dya
yogaḥ proktaḥ purātanaḥ
bhakto ’si me sakhā ceti
rahasyaṁ hy etad uttamam
Word for word:
saḥ — the same; eva — certainly; ayam — this; mayā — by Me; te — unto you; adya — today; yogaḥ — the science of yoga; proktaḥ — spoken; purātanaḥ — very old; bhaktaḥ — devotee; asi — you are; me — My; sakhā — friend; ca — also; iti — therefore; rahasyam — mystery; hi — certainly; etat — this; uttamam — transcendental.
That very ancient science of the relationship with the Supreme is today told by Me to you because you are My devotee as well as My friend and can therefore understand the transcendental mystery of this science.
Utama -> Out of Tama (darkness)
Krishna says this knowledge will take you out of darkness, Srila Prabhupad said this knowledge will be received by someone who is in position to Arjuna and that position is of being Bhakta, Why it is so, everyone requires some qualification to do something e.g. someone traveling by train requires ticket it doesn’t matter what is the degree he is possessing. You having some degree is good but for travelling in train ticket is required just your degree is not sufficient. Similarly someone may be pandit in Sanskrit but still he may not be qualified to understand sriMad Bhagwad Gita. Or someone had done Tapsya but similarly he may also not be qualified to understand Sri Mad Bhagvad Gita. Every Ekadashi I fast Nirjala ekadashi that is good but that may not make me qualified to understand BG.
The finite can never understand infinite by its own effort. There is only one way for finite to understand infinite that is when infinite reveals Himself for finite and that is possible only when one (finite) does Bhakti. When the finite living entity offers himself to infinite through Bhakti, then infinite reveals Himself by His kind will.