Matt Smith's regeneration contained a huge the Doctor a new regeneration cycle as a reward.

When Doctor Who returned in 2005, Gallifrey was thought destroyed as a consequence of the Doctor ending the Time War. Doctor Who's 50th anniversary special, "The Day of the Doctor," confirmed Gallifrey's survival, but went no further. Matt Smith's final episode, "The Time of the Doctor," subsequently revealed that the Time Lords were patiently waiting behind the cracks in time before resurfacing, and the Doctor was responsible for giving them the signal to cross through. In reconnecting with the Time Lords, however, Doctor Who also found a wonderful way to reference a classic adventure.

The Eleventh Doctor Used The Seal He Got In "The Five Doctors" During His Regeneration Episode

Always Keep A Spare Seal Handy

In order to translate the message being broadcast across universes by Gallifrey, the Doctor utilized Handles, his trusty beheaded Cyberman companion, combined with the Seal of the High Council of Gallifrey. Viewers unfamiliar with Doctor Who's classic era would likely assume this seal was just one of many random Gallifreyan relics strewn around the TARDIS' corridors. In truth, the circular treasure actually has an onscreen history from Doctor Who's past.

"The Five Doctors" aired in 1983 as a celebration of Doctor Who's 20th anniversary, and while it technically included the titular Time Lord's first five iterations, Patrick Troughton and Jon Pertwee were the only returning Doctor Who actors. The plot involved the different Doctors, their companions, and the Master being dumped into Gallifrey's Death Zone. To prove he was being sent as an ally to the Doctor, the Master was given the Seal of the High Council of Gallifrey to signify his allegiance.

Upon encountering the Master and being presented with this proof, the Third Doctor decided his nemesis must have stolen the seal, confiscated the artifact, and promised to return it to the Time Lords. Clearly, that never happened, as when the Eleventh Doctor used the seal to translate the Time Lords' message in "The Time of the Doctor" 30 years later, he briefly acknowledged, "nicked it off the Master in the Death Zone."

Why The Doctor Never Returned The Seal To Gallifrey

Did The Doctor Keep It For A Reason?

The Eleventh Doctor never explained why he kept the Seal of the High Council of Gallifrey, but doing so meshes nicely with the Doctor's established personality. Similar questions have been asked over the past 60 years: "why doesn't the Doctor fix the TARDIS' chameleon circuit?" "Why doesn't the Doctor visit Susan and his children?" The surface answer is that the Doctor is always moving from one adventure to the next, brazenly putting more mundane activities like TARDIS maintenance, visiting family, and returning lost objects on the eternal backburner.

Eleven realized very quickly that the seal could help him translate Gallifrey's message... almost as if he was waiting for the day he could put it to use.

Usually, however, there is a deeper reason behind the Doctor's apparent laziness. The Time Lord doesn't visit Susan because he's secretly scared. The Doctor doesn't fix the chameleon circuit because he's fond of the police box design. It is, therefore, possible that not returning the Seal of the High Council of Gallifrey also had a hidden motivation. Perhaps something inside the Doctor's mind told him the item would one day prove useful. Eleven realized very quickly that the seal could help him translate Gallifrey's message in "The Time of the Doctor" - almost as if he was waiting for the day he could put it to use.

Referencing "The Five Doctors" Made Matt Smith's Regeneration Even Better

A True Past-Meets-Present Moment For Doctor Who

Matt Smith's transformation into Peter Capaldi was even more significant to Doctor Who lore than prior regenerations, as it marked the first complete cycle ending. Eleven brought one era to a close, and Twelve began a whole new line. Because of that, calling back to Jon Pertwee and Doctor Who's "The Five Doctors" was a poignant way of paying tribute to classic Doctors who were part of a regeneration cycle about to be closed off forever.

Had Eleven not found the Seal of the High Council of Gallifrey, he may not have discovered the Time Lords' message in time, and Trenzalore could have been obliterated. The seal's role in saving the day almost felt like the Third Doctor reaching through time to give his older/younger self a helping hand, without which Gallifrey may not have been saved, and the Doctor may not have regenerated anew. That connection between past and present makes Matt Smith's regeneration episode work even better as an overall conclusion of Doctor Who's first regenerative cycle.