Chapel built by Seti I for his Father Ramesses I

Chapel for Ramesses I at Abydos - West Wall
Dynasty 19, reign of Sety I, (ca. 1291-1279 BCE) "earlier half of the reign, but not to its beginning" (via Brand)
Limestone, Gift of J. Pierpont Morgan, 1911 (11.155.3b)

Detail showing ankh with arms...

Further detail showing Set animal...

(From the info cards)
The Chapel of Ramesses I at Abydos
"Some fifty feet north of his temple enclosure, Sety built a much smaller but equally well decorated memorial chapel for his father Ramesses I (Dynasty 19, ca. 1293-1291 B.C.). Ramesses was probably general, and later viziet under Horemhab (last king of Dynasty 18, ca. 1321-129 B.C.) and came to the throne after Horemhab died childless. Apparently well advanced in years, Ramesses ruled for little more than two years himself. The task of building his memorial therefore became the pious duty of his son and successor, Sety."

West Wall
"The west wall is the focal point of the chapel. It is divided centrally, with scenes of Ramesses I on the right and those of his son Sety I on the left. In the two scenes from the bottom register that are preserved here, Osiris's image is replaced by the god's Abydene cult symbol."

Regarding that symbol: "Osiris also took a cult-symbol from Abdyos which is shown as a decorated box on top of a pole. It is known as the 'Abydene Symbol', but its origin and purpose also remain uncertain, although it came to be acknowledged and worshipped as the embodiment of the god." (From _The Ancient Egyptians_, by Ann Rosalie David, page 109)

"On the right, Ramesses, described as "maker of monuments in the Abydene, nome for the lord of continuity, who satisfies the heart of Onnophris with what he has desired", presents offerings to the symbol accompanied by Isis. "On the left, Sety, described as "doer of effective things for Onnophris, caretaker of the Ennead of the Sacred Land," presents a statue of himself offering a jar of myrrh to the symbol accompanied by Horus. In return for the offering, Osiris says to Sety: "My chosen son of my body, lord of Two Lands, Menmaatre, my heart is happy and content because you have acted. You are my son and protector. As long as the sky exists, your deeds will exist.""

"Rameses I must have been quite old when he mounted the throne, since his son and probably also his grandson had already been born before his accession. During his short reign (barely one year), and maybe even before, his son Sety was appointed vizier and commander of Sile but also held a number of priestly titles linking him with various gods worshipped in the Delta, including that of high priest of Seth." (_The Oxford History of Ancient Egypt_, edited by Ian Shaw, page 294)

"Sety I must be credited with the bulk of the restoration of the traditional temples, continuing and surpassing the efforts of his predecessors. Everywhere inscriptions of pre-Amarna pharaohs were restored, and the names and representations of Amun hacked out by Akhenaten were recarved." (_Oxford History..., page 295)

With this context, we can better understand the obelisk fragment showing Sety I as a sphinx with the head of the Seth-animal offering to Ra-Atum:

With the strength of Set, Seti I restores Ma'at

There's an offering table of Seti I at the Met, which he dedicated to the god Set and his consort Nephthys:

Offering Table of Seti I
New Kingdom, Ramesside, Dynasty 19, reign of Seti I, ca. 12941279 B.C.E.
Black granite, L. 105 cm (41 5/16 in). w. 53.3 cm (21 in), Thick. 15.8 cm (6 1/4 in) Rogers Fund, 1922, MMA22.2.22

Peter Brand speaks of this offering table in his _Monuments of Seti I_:

"The layout of the decoration is identical to that of the Ny-Carlsberg table dedicated to Horus, the table top being decorated with two pairs each of conical and round bread loaves and a pair of jars. On the front side, two miniature offering scenes flank the concave depression. On the right, Seti kneels with his legs splayed out and his arms upraised in adoration of Seth, who sits enthroned on a plinth. The act of the king is labeled "adoring the god four times.' Seth's figure has been hacked out in antiquity, but its outline, as well as many internal details, can easily be made out." (page 189)

This detail shows a damaged Set figure, this from the back, which is to the front.
Photographer Mark Roblee (?), (I found this in an old folder)

The front of the table with its damage was to the back when I photographed it. But here is a close up detail of Seti I adoring Set, no doubt acting as High Priest of Set:

From a photo in Brand's book

My linear clarification

Seti I expanded the temple of Set at Avaris, which Horemheb had built. Avaris later became "the new Delta residence of the Ramessid rulers" (_Oxford History..., page 295)