Complex sentence: Tommy becomes convinced that "The Gallery" at Hailsham, where the children's art and poetry was kept, was intended to look into their soulsand that artwork sent to "The Gallery" will be able to verify true love.
Split into simpler sentences: Tommy becomes convinced that "The Gallery" at Hailsham, where the children's art and poetry was kept, was intended to look into their souls. He believes that artwork sent to "The Gallery" will verify true love.