The Ascension of a Balloon
“The resurrection and ascension, supposing them to have taken place, admitted of public and ocular demonstration, like that of the ascension of a balloon, or the sun at noon day, to all Jerusalem at least.” (Chapter III)
In this quote, Paine is explaining his reasoning for disbelieving in the resurrection and ascension of Jesus Christ, which are imperative for the acceptance of Christianity as a whole. In his view, these events declare themselves to have been public demonstrations that everyone should have seen, like the noonday sun or the flight of a balloon. As it is, however, it said that few people actually saw this, and even one among their number (Thomas) didn't believe it. For this reason, Paine himself doesn't believe in the veracity of these accounts.
A Wrong Note
“Take a long syllable out of a line of poetry, and put a short one in the room of it, or put a long syllable where a short one should be, and that line will lose its poetical harmony. It will have an effect upon the line like that of misplacing a note in a song.” (Chapter VII)
In this chapter, Paine examines the makeup of the Old Testament. He says that it reeks of poetic license, and this simile helps emphasize the fact that the Bible is constructed in a way that is more concerned with art than with truth, aiding his attack on its infallibility.
Flat Like a Trencher
“The idea that God sent Jesus Christ to publish, as they say, the glad tidings to all nations, from one end of the earth unto the other, is consistent only with the ignorance of those ... who believed ... that the earth was flat like a trencher; and that a man might walk to the end of it.” (Chapter IX)
With this simile, Paine makes his argument seem sound, attacking those who believe that the earth is flat in this humorous comparison (a trencher was a wooden plate for food). He says that the Biblical message of spreading the Gospel "from one end of the earth to the other" is just bad science, proving the Bible wrong.
The Hag of Superstition
“... it is not among the least of the mischiefs that the Christian system has done to the world, that it has abandoned the original and beautiful system of theology, like a beautiful innocent, to distress and reproach, to make room for the hag of superstition.” (Chapter XI)
This quote reveals Paine's attitude toward organized religion: it has taken what is true (the fact of a God and the beauty He has created) and distorted it in a way that downplays the beauty ("a beautiful innocent") and emphasizes the depressing brokenness of the world in an attempt to control society through superstition ("the hag of superstition"). It's a cruel simile, but Paine believes in its veracity.
A Small Capital
“As to the learning that any person gains from school education, it serves only, like a small capital, to put him in the way of beginning learning for himself afterwards.” (Chapter XIII)
This quote explains Paine's views on the role of education in a person's intellectual development. He believes that the education received from schools is only the building block for further learning through experience and self-study (like a bit of money with which to make more). This school-learning is not the end of education, but the beginning.