Present participle of evangelize; the ongoing action of preaching the gospel or attempting to convert people to a faith.
From 'evangelize' plus '-ing' (present participle suffix). The '-ing' form allows the verb to function as a noun or continuous action.
'Evangelizing' is the '-ing' form English speakers use constantly for continuous actions, borrowed from Old English's '-ung' endings, but '-ing' stuck while other Old English verb endings disappeared!
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