I had a clinical death and I got back into my body only through the heels. After that I understand why the dead are carried forward with their feet and the meaning of the expression "the soul went into the heels".
From the point of view of religion.
Being highly religious people, we believe that even after death a person should be held accountable to God. During the funeral service in the temple, the coffin with the deceased is brought forward with their feet, and they are placed so that his face is directed towards the altar. In many nations, this ritual is called “the last prayer.”
The ancient Slavs believed that the door was a passage to the other world. In connection with this, there is one more "rule" - do not sleep with your feet to the door. This is due to the fact that during sleep, the state of a person, according to the ideas of the ancient Slavs, is close to death. During sleep, the soul leaves the body and goes to another world, and with awakening it returns. Modern scientists confirm that it is really impossible to sleep with your feet to the door, because during sleep a person will subconsciously understand that he is less protected and from this his sleep will be disturbing, restless.
From the point of view of tradition
The tradition goes back to ancient times, when the deceased was taken out of the house not through the door, but through a window or a specially made hole in the wall. After the funeral has taken place, this hole is closed. This is done so that the soul of the deceased would go after him and not find his way home. If this was not observed, then the spirit of a deceased person could remain in the house.
The body is also carried out with its feet forward so that the soul knows where it is being carried, but did not have the opportunity to remember the way back.
In many customs there is an opinion that the other world is “the opposite world”. Man is born head first. If, for some reason, the child is born feet forward, then the birth is either very difficult, or ends in the death of the child (less often the mother).
The custom to cover the mirrors with any cloth is also connected with this or matter. It is believed that a mirror is a window to the other world, that if the soul “sees itself in the mirror,” it can stay.
But, meanwhile, some peoples have a tradition to carry the deceased head first. "As you came to this world, you will leave." This tradition is followed, for example, by the Crimean Karaites. This is a small Turkic people who settled in Crimea.
Rational point of view.
Let's leave the issues related to religion and traditions and move on to the issues of common sense. The deceased is carried out of the house with his feet forward so that the person who carries him from behind has the opportunity not to look at the face of the deceased. Some people may simply lose their nerves at the sight of the deceased. Sensitive people can be so scared of this sight that they faint.
A living person is carried forward with his head. This is done just so that the person who is carrying from behind could assess his condition and, if anything, orient himself and provide assistance in a timely manner.
Also, according to established traditions, people who saw how they carry a person , immediately understand what happened to him - whether he is alive or dead.
The East is the place of sunrise, the birth of life. West is the place of entry, death. In the east, altars are made in churches. In a Christian funeral service in the church, they put their head to the east, feet to the west, then carry them out so that the coffin is not opened in the middle of the church. This is where the tradition started.
In ancient times, the dead were not carried through the door. The process of taking out the deceased through a window or a specially made hole in the wall was carried out. After the funeral, the hole was repaired again. According to tradition, it is believed that in this way the soul of the deceased will follow him and will not find his way home. It was believed that otherwise the spirit of the deceased could remain in the house. The deceased is carried forward with their feet so that the soul knows where it is being directed, but does not remember the way back. Some customs mention that the other world is a kind of “reverse” world. When a person is born, they go head first. Childbirth with the appearance of a baby feet forward is most often very difficult, and sometimes ends in the death of the child or mother. However, among some peoples, for example, the Crimean Karaites can be attributed to them, there is a custom to carry the deceased head first.