Speaking of Serbian characters, fyi, they are the "logical" ligatures of ль --> љ and нь --> њ .
There is also a character that was used in Church Slavonic called the "cherv" and was written as "ћ" corresponding to sounds "тъе" or "дъе." To differentiate the two (other than by intuition) sometimes in the early 19th century the "дъе" version was modified to "ђ".
For a short time, in the same period, a competing convention was to use "ль" and "нь" without ligatures as was the case for centuries; also "ть" for "ћ" and "дь" for "ђ", but the single letter solutions prevailed very early.
In addition to those letters, letter "џ", corresponding to "дж" (which is considered a single sound), was borrowed from Romanian Cyrillic. Finally "й" and the equivalent of the Greek iota (i) were replaced with "j". Thus, all sounds beginning with Я, Іо, Е, Ю, Ї (as in yield), etc. became Ja, Jo, Je, Jy, Ји (or in English Ya, Ye, Yo, Yu, Yi), hence Yugoslavia in transliteration.
For example the name Iован (Ioannis) became Јован and should be transliterated into English as Yovan. Unfortunately, transliteration into Roman characters took a turn to favor Croatian convention, resulting in some weird looking names and words.
But again, I know Bulgarian. "Који јеси¸", for example, is close to both the original "Иже еси" but also to Bulgarian "който си" (although modern grammar would be consistent with the 3rd person, "Който е"). In Serbian one can say "који јеси¸" or "који си" as in Bulgarian (except that Serbian doesn't have the definite article "то"; it would be superfluous to say "Our Father who are that..." or "Оче наш, који то јеси").
However, the "long" form yesi is an accentuated affirmative, perhaps as if saying "you truly are" as opposed to just si which is the reason the long form was retained in the prayer. On the other hand, "Който е" reflects Bulgarian loss of CS case structure (seven cases, retained in Serbian and six in Russian), which is reduced to four cases and to a Serbian ear resembles "Me Tarzan you Jane" form of speech, or in English "who be next?"
Of course in Serbian one can say that a politician "који је", a shorter form of "који јесте" (interestingly the "ь" is vocalized here as a vowel), or "који то јесте" —the "то" being equiv. to это, as in который это есть). Again, in Serbian, the longer form is always more affirmative.
In Russian the есть (the long form) also seems to be used used in the affirmative cases, and the short form doesn't exist. Grammatically the form [you] are ([ти] јеси) is the same as in CS.
["напастъ" instead of "исушение"] Where?
That should have been "искушение" (and напасть should have had a "ь" instead of a "ъ" at the end; my bad).
The Serbian Church switched to the Russain redaction of the Church Slavonic in the middle of the 18th century when the books and clergy became scarce. To fill the gap, Russian and Ukrainian clergy came to Serbia and brought service books with them which favored the conversion.
The original Serbian version of the Lord's prayer was then changed to the current one. The Serbian Букварь printed in 1597 in Venice has the Serbian redaction of the Lord's Prayer (page 7 on the PDF file).
Interestingly you can see in it that it used the form "да свєтитсє" instead of the iotated a-ligature (ia) form 
, as in "свіатитсіа" or modern "святится". See his spelling of воля (вол), which leads me to conclude that the Bulgairan and Serbian version of свети was never святий and that the "ya" somehow replaced the "e" in Russian copies and was retro-introduiced into the Serbian Church via Russian clergy in the 18th century.
Which is why you find свєщеник (in Bulgairan and former Serbian orthography, or свештеник in modern Serbian) rather than священик.
Also notice the word "царство" (a Serbian form of царствие). Also "долгы наша" are "дългы нашє", modern Serbian "дуге наше"). Likewise "не въвѣди нась".
Notice the use of "ъ" where modern Bulgarian would have them (a half-sound) as opposed to "ь" used in place of Ъ at the end of the word. Russian simply drops the "ъ" in "введи".
And finally the Bukvar says "въ напасть нъ избави нась..." where Russian would put "в" and "но".