The "to hold" bit is called the tenendum.
"Unto" is a bit unnecessary, but the purpose of the text is to show that the L is letting T hold a lease of the property.
By equipping T with the leasehold estate, L sort of devolves control to T until lease ends (term expiry, contination periodic tenancy termination, or earlier termination (by agreement or on grounds of breach) during fixed term).



