Final answer:
Harry learned from Snape's last thoughts that Snape had loved his mother, Lily, had been a double agent protecting Harry, and revealed critical information about the final battle with Voldemort.
Step-by-step explanation:
One thing Harry learned from Snape's last thoughts was the true loyalty and motivations of Severus Snape. In the memories viewed through the Pensieve, Harry discovered that Snape had always loved his mother, Lily Potter, and his actions throughout Harry's life were driven largely by this unrequited love. Snape's role as a double agent was revealed, showing that he had been protecting Harry under D___umbledore's request, in honor of Lily. This realization profoundly changed Harry's perception of Snape, moving from one of deep mistrust and animosity to a more complex understanding of Snape as a flawed, but ultimately brave and selfless figure in the fight against Voldemort. Snape's last thoughts also disclosed critical information about Harry being a Horcrux and what that meant for the final battle between Harry and Voldemort.