# What are you, great mountain? Before Zerubbabel you will become a plain

"You are nothing, great mountain! Zerubbabel will cause you to become a plain" or "Although obstacles may appear as large as mountains, Zerubbabel will overcome them as easily as one walks upon level ground"

# he will bring out the top stone

"he will bring out the top stone of the temple" or "he will complete the construction of the temple". The top stone is the last stone placed when building something. 

# to shouts of 'Grace! Grace to it!'

"while people shout, 'May God bless it! May God bless it!'" or "while people shout, 'Beautiful! It is beautiful!'"