The Book of Mormon gives us much information about what the Marvelous Work is. One of the things it tells us is that the Marvelous Work will take place among the gentiles.
See the following two references:
"And after our seed is scattered the Lord God will proceed to do a marvelous work among the Gentiles, which shall be of great worth unto our seed; wherefore, it is likened unto their being nourished by the Gentiles and being carried in their arms and upon their shoulders." (1 Ne. 22: 8)
"Yea even among the Gentiles shall there be a great and marvelous work wrought by them, before that judgment day." (3 Ne. 28: 32)
Realizing that the Great Work that Isaiah and the Book of Mormon speak about is among the gentiles, notice how the Lord reveals in section 35 that a great work among the gentiles is still a future event... this revelation was given AFTER the restoration of the church.
And it shall come to pass that there SHALL be a great work in the land, even among the Gentiles, for their folly and their abominations shall be made manifest in the eyes of all people.
Notice how three other sections of the D&C also speak of the great work that is in the future:
And from thence, whosoever I will shall go forth among all nations, and it shall be told them what they shall do; for I have a great work laid up in store, for Israel shall be saved, and I will lead them whithersoever I will, and no power shall stay my hand.
D&C 64: 33 Wherefore, be not weary in well doing, for ye are laying the foundation of a great work. And out of small things proceedeth that which is great.
- D&C 112: 6 Let thy habitation be known in Zion, and remove not thy house; for I, the Lord, have a great work for thee to do, in publishing my name among the children of men.
All four of the above revelations were given AFTER the first vision, AFTER the restoration of the two priesthoods and AFTER the restoration of the church.
From these scriptures it is apparent that the restoration of the Church back in the 1830's was
laying the foundation in the 2nd watch, for the Great Work that would come forth at a later time in the
third watch!