This could mean that your freeholder has, as per his or her legal obligation under the 1987 Act. offered the leaseholders of the building the opportunity to purchase the freehold under the so-called ‘right of first refusal’ under that Act.
Why would the Freeholder offer the Freehold to the Leaseholders?
It could be that the freeholder has a potential buyer or other plan to sell the freehold but if he does not offer the freehold to the residents first he may be committing a criminal offence. This is an opportunity to come together collectively as Leaseholders and acquire the freehold.
You may already have the right to buy the Freehold under the terms of Collective Enfranchisement, but receiving a notice is a good impetus to starting the process.