Inorder to save man from Sin and evil, God came into this world as the seed of a woman as he promised to our first mother Eve while she was in Eden, after committing sin.
Salvation is to reinstate man as how he was in Eden.That is the historic destiny of man. God knew that man cannot be separated from sin / evil by his own.
As a loving father the merciful God revealed himself to the humanity in incarnation.
He came into this world in the midst of the history. Thus He proclaimed the salvation to the people of
Through cross He died and just like one of us in spirit he went into Hades and proclaimed Salvation to the departed souls.
Before his death, through His disciples He instituted Holy Qurbana to fulfill the prophecy in scripture, that he is IMMANUEL. That means God with us. He instituted the Holy Qurbana and entrusted His disciples to do it until He comes. Through them it continues. Thus we see Him in our midst.
Now the process of salvation is complete. He came. Proclaimed the salvation to the people of that time. Went back to the departed ones and gave the hope of salvation. Now Thru Qurbana He lives with us.
Whether it is the real one or not you have to look into the apostolic succession. If any discontinuity is there in any denomination in apostolic succession we cannot have Communion with them. For that we need one faith. One baptism. One confession. And the apostolic succession.
To us every tablet (medicine) seems to be same. For cure we don't take these tablets as we feel. The wrong one will be poisonous . It is all tested and defined by scientists. Even though the Doctor is the one who prescribes, heis allowed to treat the patient according to what he was taught and not by his own intuition.
A wrong prescription can kill many.
"But let no one eat or drink of this Eucharistic thanks giving , but they have been baptized into The name of the Lord: for concerning this also the Lord hath said : Give not that which is holy to the dogs.? Didache 9:5