Isa Upanishads indicates that: By worshiping gods and goddesses and going to the world of gods after death is of no use.

Isa Upanishads indicates that: By worshiping gods and goddesses and going to the world of gods after death is of no use.  The time one spends in ritualistic practices is wasted; one can spend the same time moving forward towards Self-knowledge, which is the main goal. One cannot reach the non-dual destination by glorifying god and goddesses and by doing that, one goes deeper and deeper into the darkness. It surely indicates the fact that, the seeker of truth has to drop the worshiping god and goddess in order to get self-knowledge.

It also indicates that, Religious Rituals (Avidya) is Karma (action) and therefore a hindrance. By performing Agnihotra and other sacrifices (Avidya) is a roundabout way of purifying the mind, and it is also groping in the dark.

In addition, it indicates the karma is limited only to the religious rituals, not on the whole human life. This karma theory based on the human conduct must have been adopted from Buddhism and other theories based on human conducts. 

When it says: Perform the obligatory karmas without any attachment to the fruits, and at the same time worship gods and goddesses, again without any desire to go to heaven - then you can get the benefit of both, liberation and bliss. For those who are not yet ready to renounce, this path is recommended, it means that the religion and its  idea of god and goddesses and code of conduct, and its rituals are meant for the mass who are incapable of thinking of the beyond.

In addition, it also speaks of heaven the abode of gods, where one goes after death, and it speaks of rebirth, this contradiction, seeker has to conclude that religion, rituals god and its code of conducts are meant for the mass that is not receptive to self-knowledge. 

When the self is not the body whatever one sees, knows, believes, experiences and feels on the base of the body as self is bound to be an illusion.  Thus, the karma performed in illusion is bound to be an illusion. The birth, life and death are happening within the illusion, therefore it is bound to be an illusion. Thus, rebirth and reincarnation theories based on the false self within the false experience are bound to be an illusion on the base of the true self. Only the witness of the illusion is real (Brahman).  Therefore, everything has to be viewed and judged, on the base of the Formless Witness (soul) in order to overcome the illusion/duality. 

Seeker of truth has to know somewhere he is going wrong, and it is for the seeker to go on his own and remove the obstacle.  The greatest hindrance is mixing religion, god, scriptures, and yogic theories. Moreover, attachment to scriptures, personal god and religious code of conduct keeps one permanently in the grip of duality.