Does anybody know classical Chinese?

It'll be quite difficult to translate the letter word for word. But I believe the general meaning of the letter is:

The emperor of Mongolia wants the king of Japan to know that he (and his ancestors) are the mandate of Heaven and they have the power to control the fate of their neighboring countries (ie. Korea was spared because of Mongolia's "generous" decision to cease file). The emperor of Mongolia sees their relationship with Japan is "like father like son". However, because Japan is close with Korea and China, the emperor of Mongolia wonders why Japan has yet to know that the new emperor has taken his throne and why no ambassadors have been sent to pay respect and warns that Japan should comply (ie. send ambassadors over and enter into a friendly "ally" with Mongolia") or else...

Basically, the emperor of Mongolia is using this letter to demand Japan to become a state of Mongolia, just like Korea, and if Japan refuses, Mongolia will have to resort to arms.

was there any punctuation or anything?...
it's divided to lines just at random...
here it's as a readable variant...

上天 眷命

大蒙 古国 皇帝 奉书
日本 国王

朕 惟 自古 小国 之君
境土 相接 尚务 讲信修睦 况 我祖宗
受 天明命 奄有 区夏 遐方 异域
畏威 怀德者 不可 悉数 朕 即位 之初 以 高丽 无辜 之民久瘁
锋镝 即令罢兵还其 疆域 反其 旄倪 高丽
君臣 感戴 来朝 义虽君臣欢 若 父子 计
王之君臣亦已知之高丽 朕 之
东藩也 日本 密迩 高丽 开国 以来 亦时通 中国 至于 朕
躬而无一乘之使以通 和好 尚恐
王国 知 之未审故 特遣 使持 书

布告 朕 志 冀 自今 以往 通问 结好 以
相亲 睦且 圣人 以 四海为家
不 相通 好岂 一家之理哉 以至用兵 夫孰 所好

王其图之 不宣

至元三年八月 日

i don't know 文言 vocabulary but it's something about ancestors, establishing the state of Korea and hope to keep in touch with each other...
doesn't look authentic for me...
perhaps coz i was able to read it...
or coz there is smth missing between 月 and日 (last line)

if i couldn't read a word then i'd think "whoa, that must be a real ancient scroll"...
but the main idea of this royal SMS is pretty clear...
:)

On life天眷
Great book from the emperor of Mongolia
King of Japan since ancient times a small country but I King
Throughout the soil phase works still speak the status of my letter Xiumu
Ancestors suddenly ordered by the district Tianming summer ya side differences
Huaide畏威domain I that is, not to the full
Bit at the beginning of the innocent people of Korea in the long weary
Dysprosium front of their boundaries to make the anti-罢兵also its aged Ni Korea
Jun-chen to wear to a sense of justice, although North Korea if the son of Huan-Jun-chen
Jun-chen Wang Korea is well known to the I
East Japan fan also close to near the founding of Korea
China is also the time to pass without regard to朕躬
Ichijo's so good not to pass and may
The Kingdom of the trial they did not know who book special envoy
I notice from this past Zhi Ji Tong asked knot
Harmony and good to love for the saints to the world
How can families do not share a good reason and Weizai
Which troops Cardiff gave
Wang has not announced its plans
Yuan in August on a three-year


Hope this helps. Some words i couldn't translate