It has been a precious privilege that he was able to ... Write what I have = Write the things I have written In the various articles = He has written these things in various articles Tendered in evidence against me = Presented as evidence in a court case against the writer. He has written things in various articles. These articles are used as evidence against him in a court case. It was a pleasure for him to write the things he wrote in those articles.

to show or reveal evidence against. -This extract is written very lofty and old-fashioned.- Not natural to modern English speakers.

his articles proved his crimes but he was glad he wrote them