The Buddha is not a vegetarian, and he did not teach his disciple to be vegetarian. Instead, he taught them to have a mind of great compassion. To be compassionate, one should be honest, kind, grateful, empathetic, generous and avoid hurting all sentient beings as much as possible.
The first precept of Buddhism is to refrain from taking life. But in reality, that is not possible. Animals have been killed to provide leather for bags, rendered fats for soap, gelatin for medicine, and many other daily products consumed by humans. Even if one only eats vegetables and fruits, he/she is indirectly responsible for encouraging farmers to use insecticides and poisons for their crops. Hence, to practice the first precept, one should avoid directly killing these sentient beings.
Nevertheless, being a vegetarian is still ideal because all animals have Buddha nature. They, like human, have the desire to live and fear death. Everyone faces the causality of the three periods of time - past, present and future. If we eat meat in the present, the suffering and pain we have inflicted on the animals will eventually be inflicted upon us in the future.
For people who are unable to become pure vegetarian due to family, work, health or other issues, they can choose to avoid meat consumption on the first and fifteen day of the lunar calendar, or on the six vegetarian day (8th, 14th, 15th, 23th, 29th, 30th day of the lunar calendar; 28th and 29th for months with 29 days). If one has to eat meat, one can consume the "three clean meats". Only meat that fulfills the three requirements can be allowed to be eaten.
- Not seeing the animal being killed. This means that we should refrain from buying live fish/animal in the market and getting the fish monger/butcher to slaughter them for our consumption. This also includes fishing or hunting.
- Not hearing the animal being killed. This means that if we can hear the agonizing cries of the animal being killed, we should not eat the meat.
- Not being suspected that the animal is killed for us. This means that we should refrain picking live seafood in restaurants, because we are directly selecting them to be killed for our consumption. Or if we know that certain cultures will kill a goat/cow for a banquet to welcome us as guests when we visit, we should reject the meat.
To truly achieve the purpose and benefits of being a vegetarian, one must first have a mind of compassion, which should be practiced in all aspects of one's life. Having the right intention is very important. Only then would one be able to gain infinite merits and blessings. If one is a vegetarian, but likes to steal, cheat and hurt others, one gains bad karma, instead of merits.