You dont need to watch The End of Evangelion to understand episode 25 and 26. The End of Evangelion was the original 25 and 26, but the director decided to practically ruin the series because of all the death threats and letters he got from the fans. The end of evangelion shows what really happens with the human instrumentality project coming into action, and so did Death and Rebirth. Episodes 25 and 26 are not open to different interpretations, they only represent one thing : the director's schiznophrenic episodes and his mental illness (his nervous breakdown). Pretty much the entire show is based off that. Symbolism? The Spear of Longinus (the spear that pierced Jesus Christ's heart), The MAGI (the wise old men), the Tree of Life (the Sephirothic system), Rei, Shinji and Asuka representing the Ego, Superego and the ID (not in particular order), all that stuff was added just to make the series look good and help in construct the plot. That is not symbolism. The show is still worth watching.