Now that I know you're a unbeliever I will take my time. First and foremost a Christian foundation is Gods word only. All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness:17That the man of God may be perfect, throughly furnished unto all good works. 2timothy 3;16-17. To understand death, you must understand the creation of man. Genesis 2;7 states, And the LORD God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul. When God formed man he had a heart, a lung, brain, and etc. But he could not get off the ground! Why? Bible says acts 17;28 For in him we live, and move, and have our being; as certain also of your own poets have said, For we are also his offspring. God is the source of life. That is what the creation of man teaches us. When we die the physical body is lifeless like Adam before God gave him life. The creation doesn't teach of spirit or ghost. Furthermore, the belief of the immortal soul or spirit is from Satan! It started at the garden of Eden Genesis 3;4 in that is the basis of modern spiritualism. The state of the dead is important to know! When you believe other than what the bible teaches then you open yourself to his deception. This is Satan tool as it work the ruin of Adam and Eve in the garden. That is why your seeing spirits the devils is manifesting himself to you because your not grounded in the word of God. Sorry for the next quote it is long but necessary. The doctrine of man’s consciousness in death, especially the belief that the spirits of the dead return to minister to the living, has prepared the way for modern Spiritualism. If the dead are admitted to the presence of God and holy angels, and privileged with knowledge far exceeding what they before possessed, why should they not return to the earth to enlighten and instruct the living? If, as taught by popular theologians, the spirits of the dead are hovering about their friends on earth, why should they not be permitted to communicate with them, to warn them against evil, or to comfort them in sorrow? How can those who believe in man’s consciousness in death reject what comes to them as divine light communicated by glorified spirits?Here is a channel regarded as sacred, through which Satan works for the accomplishment of his purposes. The fallen angels who do his bidding appear as messengers from the spirit world.While professing to bring the living into communication with the dead, the prince of evil exercises his bewitching influence upon their minds. GC88 551.2
He has power to bring before men the appearance of their departed friends. The counterfeit is perfect; the familiar look, the words, the tone, are reproduced with marvelous distinctness. Many are comforted with the assurance that their loved ones are enjoying the bliss of Heaven; and without suspicion of danger, they give ear to “seducing spirits, and doctrines of devils.” GC88 552.1
I hope this is helpful?