We have two sources for acquiring spiritual knowledge.
Philosophies are works of human beings who tried to understand the realities around them, who tried to find answers to questions like who are we? who is God? what is the purpose of life? etc
The problem with philosophies is that every philosopher gave a different explanation for these questions. For example – philosophies of Buddha, Mahavira, Shankaracharya, Ramanuja, Madhvacharya are not only different from each other they contradict with the other on many important points.
Buddha rejected soul (Atma), mahavira accepted it (each human has a soul), Shankaracharya’s adwaita says soul in all living beings is ONE and that is Brahman (God) and so every individual is actually God, Ramanuja rejected this and said Brahman is like sun and individual souls are like rays (sun self illuminating, rays depended on sun), Madhvacharya said individual soul and Brahman are different.
Buddha, mahavira rejected the notion of God where as others accepted Brahman but defined it in entirely different ways. For shankaracharya its nirguna, nirakara, sudha chaitanyam (attributeless, formless, pure consciousness) where as for Ramanuja its saguna, saakara (with attributes, with form) and he equated Brahman with Vishnu and Madhvacharya said Brhamn is Krishna.
Similarly you will find contradictions in path to salvation, the very definition of salvation and what happens after salvation etc.,
PHILOSOPHERS ARE HUMANS AND THEIR KNOWLEDGE IS LIMITED AND THESE VARIOUS PHILOSOPHIES ARE PROOF OF IT.
There is an alternate source of spiritual information for those who are interested. Its called REVELATION. Here God is sending down a message to His chosen men, giving us the knowledge of reality of life and beyond. Quran is a perfectly preserved revelation available to us.
No matter how great a philosopher is, he cant tell us what happens after death, all they did was some predictions. God, almighty, all-knowing knows future also., he is communicating to us through Revelation about all the facts of life.
Please read Quran to understand the message of Revelation.