The main teachings of the Bhagavad-Gita are:
Be compassionate towards all living beings, thus love all living beings. This means don’t be envious or hateful of others. Be friendly to others, be nice to others, be kind to others, be generous to others, be merciful to others, be charitable to the needy. Don’t cheat others, don’t lie, don’t steal, don’t hurt others, don’t drink, don’t take drugs, don’t eat meat.
This body you (the soul) are residing in, is temporary, but the real you, the soul, is eternal. Just as we change worn out clothes, jobs, houses, cars, partners, and so on. One day you will be forced to change your body too. So don’t get too attached to this temporary body and material life. And just as a manufacturing company designs it’s products today for production in the future. Similarly you are designing your next body with the actions you are taking now. So if you think let me enjoy now and forget about the future. Thus if you think your next life is not worth thinking about now. Then your next life will be that of nothing. You will take birth among the 8 million species of living beings below that of human beings (animal and plant kingdoms) and be trapped yet again in the cycle of reincarnation.