From what I know about Christianity, you would probably find it difficult to reconcile the views about human nature.
Freud thought there are three instances of the human mind: Id, Ego, Superego (or in another (or the conscious mind, the preconscious mind and the unconscious mind in another classification).
The Id is considered the source of our impulses and instincts, especially those sexual and aggressive. There is nothing about being good, evil, believing in God or not. The Ego and Superego are formed later as a way to contact the external world and make existence in the society possible- put it this way, at Id level, the only thing that matters are for those drives to be satisfied (if you want, the only thing that the Id seeks is pleasure). But pretty obviously it would make life in a group impossible.
Now, Superego would be the instance that encompass our moral values, religious morals, the laws (written and unwritten), etc. The Ego would be the instance that tries to “mediate” between Id, Superego and reality. Lets say a married person find their boss sexually attractive. At Id level, stuff like being married or being your boss doesn’t matter, there are only the sexual impulses to be gratified. Superego would deem any action or thought unacceptable. The Ego might try to solve the issue by “letting” the person next time to paint a romantic painting with maybe a certain resemblance to their boss (considering the Ego uses sublimation as a defence mechanism) or the person represses that sexual impulse and it might appear in their dreams.
Now about religion- Freud thought it had it’s role somewhere part of the Superego. The useful role was to work on preventing violent impulses to be “unleashed” in a socially unwanted way. Plus it also gave people hope and some sense of understanding when science failed to do so. But if this is all the role religion has- obviously you can argue (and he did) that there are other ways- like science/knowledge to obtain a similar result.
And the elephant in the room here is that if our Ego works so hard to “mediate” between the drives of Id so that they won’t get satisfied in a dangerous or unwanted way, and the demands of the Superego (and the resulting anxiety or guilt) that it might be harmful to add “extra demands” on Superego