How do Baptists interpret the summoning of Samuel by the medium of Endor?

While it is true that the Baptist faith does not specify many things in which there are rigid specifics for belief; that is based in the belief that the holy Ghost will teach each person how the specific parts of the Bible apply to them individually. That belief is fostered by Jesus saying in:

John 14:26 KJV But the Comforter, which is the Holy Ghost, whom the Father will send in my name, he shall teach you all things, and bring all things to your remembrance, whatsoever I have said unto you.

That having been said; In my 50 plus years as a Southern Baptist I have never heard of any official doctrine concerning this specific incident, but have been privileged to be a part of several discussions concerning the general subject, and there are some observances which may help to clear up this for you.

The General belief as far as I can determine is that the absent from life, present with the Lord idea pertains only to those who die after Jesus arose. The reasoning here lies in the fact that until Jesus suffered death for his believers death still reigned upon the Earth

Under that precept Samuel would still be sleeping in the Grave awaiting the arrival of Salvation. Therefore, the Soul which the witch of Endor recalled was neither in heaven or in Hell, but was sleeping.

Hope this helps.

These two Scriptures may help you to understand the difference between sleep prior to Jesus sacrifice and after.

John 11:11 KJV These things said he: and after that he saith unto them, Our friend Lazarus sleepeth; but I go, that I may awake him out of sleep.

Luke 23:43 KJV And Jesus said unto him, Verily I say unto thee, To day shalt thou be with me in paradise.

These words of Jesus give us much insight into the concept of Jesus as the central point of salvation both in the Physical realm and in the Spiritual Realm. In John what we see is that Lazarus is still subject to the physical realm in that Jesus has not at this point conquered death, but does have power over death in that he has the ability to bring Lazarus back to life in the physical realm. On the other hand what we see in Luke is that Jesus is declaring that he is presently going to overcome death and usher in a complete and different set of rules not only in the physical realm, but also in the Spiritual realm.

This question is almost impossible to answer, as stated. As Baptists (by definition) have no unifying system of doctrine, the denomination as a whole has not made any kind of statement about how they deal with particular items, with the notable exception of baptism. That is to say, you'd have to ask each Baptist individual to find out what they believe.

That being said, there are other denominations which believe similarly (that the faithful are immediately united with God upon death) and DO have a unified system of doctrine that you might be able to query.

Some focus on Samuel's words "brought me up" to argue that he was not "coming down from" Heaven, but was "coming up from" Sheol (they argue that Sheol was a common holding place for the general dead and part of Jesus' purpose in "descending into Hell" was to bring the faithful our of Sheol and into Heaven, to bring them into the reward they had anticipated in the longed-for Messiah). Consequently, Samuel wasn't removed from God's presence, but merely from Sheol.

Others (who believe that the faithful have always gone to Heaven) argue that Endor's surprise was because the summoning was genuine, implying that she was a charlatan, and that God performed a unique miracle in this one case. She didn't expect it to work, and was shocked when it did. In which case, there doesn't seem to be any difficulty in claiming that God miraculously a genuine apparition of Samuel to Saul for this one purpose. They focus on Samuel's words "why have you disturbed me" to imply that wherever he was, was a place of peace and rest from which he could be disturbed, which can be said of neither Hell, nor Sheol, nor Purgatory.

There are still others who make a distinction between Abraham's Bosom and Heaven, as well as between Sheol and Hell. They claim that Abraham's Bosom was like a pre-Heaven, and Sheol was like a pre-Hell, and that when Christ died those two passed away and were replaced by Heaven and Hell respectively. I don't understand enough about this idea to say much more, but it is out there.

John Calvin wrote in his commentary that it was Satan who was pretending to be Samuel. I find this difficult to reconcile with the prophetic truth of Samuel's words, so I'm inclined to believe that it was either genuinely Samuel, or it was an angel who Saul mistook for Samuel (note that he never claimed to be Samuel).