Seraph

Changed Loyalties

Seraph used to protect the Merovingian, but now protects the Oracle:

• When Seraph, Morpheus and Trinity entered Club Hel, they killed a bunch of bodyguards who could walk on the ceiling. One bodyguard outside of the club called Seraph "wingless" just before engaging in a fight, implying that Seraph used to have "wings" like they did (or, what appears to be the ability to alter the direction of gravity as it applies to them).
• When the three enter Club Hel and the Merovingian sees them, he says, "The Prodigal Son returns" (an obvious implication that Seraph worked for him) as well as, "L'ange sans ailes" (French for "the angel without wings"). I think the Merovingian is the one who removed Seraph's "wings," probably by programming a virus into a piece of food that Seraph ate which destroyed the code in him that allowed him to defy gravity. This would also explain the exchange between Seraph and Trinity before they broke into Club Hel. Seraph says, "We should return to the Oracle. She will know what to do." Trinity responds, "No. We know what has to be done." Morpheus then looks at Seraph, bringing our full attention to Seraph's reaction, and Seraph reluctantly turns his face back to the road as he is driving, realizing that Trinity is, unfortunately, right.
• When the three walk upstairs and begin negotiation, the Merovingian calls Seraph "Judas," clearly implying betrayal.

Why does the Oracle need protection? The Oracle is a unique program in the way that it is not invisible to people inside the Matrix. As the Oracle says herself, programs that are functioning as they should are invisible when they’re doing their job (programs governing birds, weather, etc.). But the Oracle isn’t one of those programs. Because of her unique purpose of guiding the One (and perhaps because she is also going beyond her job description - she is playing what the Architect calls a "dangerous game" by interacting with hackers and manipulating the future), she must live in a physical shell inside the Matrix, and she is therefore more vulnerable inside the system than other programs. That is why the best protection is necessary, even for the Oracle, who can see pretty far into the future.

Forever Indebted

When the Merovingian was protected by Seraph, it would have been for the same reason as the Oracle: the Merovingian was a unique program in the way that he was not invisible to people inside the Matrix. When the Merovingian was scheduled for deletion, Seraph probably was too, and both became exiles. This would have made Seraph even more of a "slave" to the Merovingian than he was before, because just like any other exile under the Merovingian's control, the Merovingian guarantees their protection from system restarts in exchange for their loyal service, whatever it may involve (including crime).

In ETM, Seraph says he is forever indebted to the Oracle. What this probably means is that the Oracle named Seraph her protector sometime after Seraph had become an exile. In other words, the Oracle removed Seraph's exile status and reinstated him with purpose within the Matrix system. She literally got Seraph out of machine hell.

Smith is right about purpose - it drives, binds and guides programs. Even more than that, purpose is the only reason programs are allowed to survive. If a program's purpose is outdated, the system determines that the program is to be deleted. To reinstate Seraph's purpose within the system is to give Seraph everything that matters. Thus, he truly is "forever indebted" to the Oracle. He no longer has to depend on the Merovingian to survive system restarts.

I assume the Oracle wishes for something similar for Sati, to have her identity validated by the system assigning Sati a purpose. Or, perhaps the Oracle wishes for another step of evolution on the part of machines: to allow for purposeless existence.