Lamb
Lamb is actually a symbol for God. It is also a stock image of pastoral poetry.
Thee
Especially a term of pastoral poetry for the pronoun 'you'
Bid
To give something open heartedly
Mead
Meadow; A wide grassland
Wooly
Tender; soft; comforting
Tender
Very soft and fragile
Vales
Valleys; Long stretch of lowly grassland between hills
Meek
Gentle at heart
Dost
In pastoral poetry "do" is written in this archaic form to signify a scene of a long past.
Rejoice
In pastoral poetry it means causing joy to someone. Here the lamb's voice is the cause for the rejoicing of the valleys.
