To travel spiritual path successfully Bhagavad Gita advocates our indulgence in Sattvic attitude all throughout. A Sattvic attitude means living godly life and invoking positive thoughts all the time. Once who is Sattvic, to invoke positive thoughts most of time is a pure vegetarian.
Non-vegetarian diet at times invokes impure thoughts. This results from killing of animals. When innocent animals get killed for the sake of human consumption, someone is a sinner in the whole cycle. By consuming non-vegetarian food we become a party to the killing.
For a sattvic person delicacy in food, eating habits was never an end in itself. A sattvic person consumes food only to maintain his body whereas a Rajasic person sometimes lives for the sake of food. Our attraction towards food distracts us from our spiritual goal of life.
Lord Krishna in Bhagavad Gita advocates a pure sattvic food was essential to invoke pure thoughts. Consumption of non-vegetarian food at times carries with it the stigma of sin. We may not have directly killed the animal consumed as food but indirectly we were also responsible for it.
Vegetarians on path of pure spirituality always invoked positive thoughts. No feelings of killing, bloodshed existed with vegetarians. Becoming a vegetarian, living a vegetarian lifestyle is kingly. Not all can afford it. Those dominated by ego failed to understand precept of spirituality in totality.
In present times when vegetarian food is available in galore, why go for non-vegetarian food and delay our spiritual journey. Unless we lived in tundra region, where absence of vegetation is conspicuous and wanted to indulge in spirituality, there was no alternative than to consume non-vegetarian food. The spiritual journey of such people still would get delayed.
While vegetarian food is important for spiritual travel can be gauged from the fact that in erstwhile Bharatvarsha (now India) hundreds of seekers succeeded in reaching God. Comparatively in West only Jesus Christ and Prophet Mohammed reached state of enlightenment. The entire jnana wisdom of Jesus Christ and Prophet Mohammed is owed to teachings of Bhagavad Gita and Upanishads (independent spiritual treatises), even Vedas (Hinduism revelations).
I am 100% positive that since the time Jesus Christ and Prophet Mohammed started their indulgence in spirituality, they became pure vegetarians.