To the devas go the worshippers of the devas; to the pitris go their votaries; to the bhetas go the bheta worshippers. My devotees come to Me. (Bhagavad Gita Chapter 9 verse 25)
The devas are angels or gods or bright spirits who in a celestial sphere enjoy the merits of their good deeds performed during earth life. They have a subtle body and can travel with the velocity of thought, just by their will power. Not encumbered with a gross body, they do not suffer from heat and cold or hunger and thirst. Neither are they ever fatigued. No sorrow, no depression, no suffering ever enters their world. There, hatred and envy and jealousy are not entertained. These are barred from the gates. It is the pleasure garden where all enjoy eternal youth. The gods are said to have the power of granting boons to their votaries as they have charge of certain forces in the universe. They enjoy adoration. And when they find on earth devotees who regard them very highly and who bring offerings to them, they are much pleased and they give the votary whatever he most desires.
Now, when a person prays to these devas and constantly worships them and at the same time lives a righteous life, when he dies he joins these gods in their heaven and he becomes one of them. And there is a continuous entering and departing from these heavens, the same as on earth. For though the gods may enjoy their heavenly abodes for long years, the end must come at last and they enter earth life once more.
It is the same with the spheres of the pitris, the ancestor world where ancestor worshippers go, and also with the sphere of the bhetas (beings between men and devas) commonly called spirits. But what is more important than all this is that those who worship Bhagavan go to Him. But what do we find? Notwithstanding that it is no more trouble, people do not worship Me alone, says Bhagavan, because of their ignorance. That is why they attain very small results. The trouble, the effort, is the same, whether we direct our worship to a deva or a pitri or to Bhagavan. On the other hand, the results are very different. For though all other paths bring small results and lead to temporary happiness, only the worship of the eternal One results in the highest good, namely everlasting bliss. From there, no one has to return. Once with Bhagavan means eternal union with Him.