A big chunk of The Punisher is focused on Frank Castle, Micro, and Dinah Midani investigating a shady military organization — snooping around alleys and apartments to get names and plan out strategies to finally uncover the truth and take down the intra-military terrorist cell — but the show changes up its format in Episode 10. The set-in-one-day episode is a climactic one in the new series; one in which all the main characters finally intersect around a major event. To make things even more intriguing, Episode 10 begins with a symbolic scene between Lewis and some birds. It is such a strange break in character for Lewis Wilson, the young veteran who we've seen become more and more unhinged to a dangerous extent due to being unable to re-assimilate into civilian society, but the bit of warmth he shows the birds in the apartment of the man he just killed has a deep meaning for Lewis.
Episode 10, entitled "Virtue of the Vicious," centers on Lewis' major terrorist act. After having bombed a couple government buildings and sent a letter to Karen Page outlining that his frustration with the government at large and more specifically anti-gun laws are what is motivating his attacks, Lewis comes up with a daring plan to attack a prominent anti-gun senator along with Page during an interview at a hotel. To get into the hotel undetected, Lewis first kills an agent at Billy Russo's private security firm Anvil (who was hired to protect the senator during the interview) and takes his uniform. But before he snags the guy's Anvil uniform, Lewis notices two birds in a cage near the dead man's window. Lewis walks over to them, opens the window and then the cage, and taps and chirps at them to attempt to get them to fly away. But the birds remain in the cage. It's a powerful bit of symbolism for Lewis' story, as well as some foreshadowing to how he will meet his end later in the episode.
The birds in the cage seem to be a clear reference to Lewis' life within the military, and how impossibly hard he has found re-assimilating after returning from his service. When Lewis came back from war, his metaphorical cage was opened, but Lewis did not know how and did not want to leave his military life. He dug a foxhole in his backyard rather than sleep in his own bed, trying to build another "cage" of his own to escape civilian life.
And the symbolism of Lewis and the birds goes even deeper than just mirroring his inability to re-assimilate. They also serve as a stirring bit of foreshadowing to the end of Episode 10, which culminates in Lewis' death. After strapping a bomb to himself and taking Karen Page hostage, Lewis regales Page with the advice he got in the army that he still repeats to himself often:
Remember it is ruin to run from a fight. So take open order, lie down, and sit tight. And wait for support like a soldier. Wait, wait, wait like a soldier.
Just sitting around and waiting — sounds a lot like those birds, doesn't it? The foreshadowing of the birds in the cage goes even further after Page is able to free herself from Lewis and he locks himself in fridge before the Punisher can shoot him. The last moments we see of Lewis are of him in the place he always wanted to be: another big cage. In the end, Lewis decides to detonate the bomb and kill himself while he's in the fridge. Like those birds, he just couldn't imagine leaving.