[Pelham]

If that is the case wouldn’t Lincoln have stated that his purpose was the need to protect the Fort and its troops rather than saying it was because of the inability to collect revenues?

We should go on what he wrote in his proclamation. It was important enough to him that he leads with it in his opening paragraph.

[BroJoeK]

Pelham: "If that is the case wouldn’t Lincoln have stated that his purpose was the need to protect the Fort and its troops rather than saying it was because of the inability to collect revenues?"

No, we are talking about "before Fort Sumter" versus "after Fort Sumter", meaning the Confederate military assault on April 12.

Before April 12, Lincoln's mission was strictly to resupply Union troops there.
After April 14, everything changed and Lincoln's mission became what his public messages said -- to suppress the rebellion and collect tariffs, etc. Really, this is not rocket science, if you simply remember that the Confederate military assault on Fort Sumter was just as much a Game Changer as was the Japanese attack on Pearl Harbor, December 7, 1941.