Complex sentence: He entered the diplomatic service of the Holy See in 1973, and worked at the papal diplomatic mission in Iraq and Great Britain and then, from 1978 to 1989, the Secretariat of State.
Split into simpler sentences: He entered the diplomatic service of the Holy See in 1973. He has completed his work at the Pontifical Representations in Iraq and in Great Britain, then from 1978 to 1989, the Secretariat of State.