For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
The very name of the devil is "accuser of the brothers" (Rev 12:10). This he does "day and night." Christ counteracts it by His advocatory ministry which He keeps doing "forever" (Heb 7:25).
The devil is a non-stop accuser whereas Christ is the never-ceasing Advocate in heaven! Alleluia! As we are living in the era of Holy Spirit, He is the defender," "the advocate," as well as the "mediator" who fulfills the function of intercessor on this earth.
There is no other saint can be our mediator. Mary cannot be our mediator either.
God would not answer Saul either by dreams and visions, Urim and Thummim, or by prophets, for He had departed from him and had taken the Holy Spirit away from him because of sin (1Sam. 28:6, 15- 16; 15:26; 16:13- 23; 1Chr. 10:13- 14). If God had refused to answer him by legitimate means, He certainly would not answer contrary to Scripture (Lk. 16:26). If He would not answer by the Holy Spirit, He certainly would not answer by a demon seeking to imitate Samuel (1Sam. 28:7- 19; 1Chr. 10:13- 14). It is clearly stated that Saul sought information from demons, not from God who refused to answer him. He specifically wanted a witch that had a familiar spirit, to inquire of her (1Sam. 28:7). His request was for her to divine by the familiar spirit (1Sam. 28:8). The Bible plainly teaches that communication with the dead can be demons imitating departed loved ones (1Sam. 28:7- 19; Dt. 18:11; 1Chr. 10:13- 14; Isa. 8:19). It is commanded in many scriptures not to traffic with demons or seek communication with the dead (Lk. 12:29); therefore, God would not allow Samuel to communicate through a witch. The seeming appearance of Samuel to the witch was simply the familiar spirit imitating and impersonating him (1Chr. 10:13- 14). When it appeared that Samuel was speaking to Saul, it was the demon speaking; it would know about both Samuel and Saul and their past relationship. Such a demon could also make predictions (Dt. 13:1- 3).
Isaiah warned later that those who sought the dead were deceived by familiar spirits (Isa. 8:19). The demon practically revealed his identity when he said that Saul and his sons would be with him tomorrow. Saul went to the torment compartment of sheol or hades, whereas Samuel went to the comfort side of the underworld of departed spirits. See Where Are the Dead? And Hell in Where Are the Dead?.. There is no record of God seeking to intercept the communication of demons and men. Saul inquired of a demon and was answered by one. When God gives answers His messages come only through the Holy Spirit in different ways, but never through unlawful or unscriptural ways, as here. The case of Balaam is sometimes mentioned as proof that God intercepts messages of Satan and utters His own through the same channel, but this is not true. Balaam was a true prophet as long as he was used by God.
It is stated in 1Chr. 10:13- 14 that Saul died for his previous sins and also for sinning against the Word of the Lord (which forbade witches and traffic with demons, and for asking counsel of one that had a familiar spirit) and not inquiring of the Lord (on this occasion). Thus, it was from a familiar spirit, and not Samuel, that he obtained his information.
Jesus taught that it is impossible for the dead to communicate with living persons on earth, and all scriptures on the subject of the state of the dead, and on heaven and hell, completely confirm His teaching..The only case of any person leaving his place of confinement between death and resurrection is the case of Moses whom God brought up for a purpose, on the mount of transfiguration (Mt. 17:1- 8). We must bear in mind though, that this was an act of God and not a demonized witch or wizard. Hence, we conclude that 1Sam. 28:7- 19 is the record of a demon impersonation.