Congratulate, Congratulation

The verb ‘to congratulate’ has its origins in the Proto-Indo-European (PIE) root gwere- (2) (to favor), Latin gratus (agreeable) and Latin gratulari (to give thanks, show joy). Latin com- (together, with) + gratulari = congratulari (to wish joy). ‘To congratulate’, meaning to address with expressions of sympathetic pleasure, is from the 1540s.
 
The noun congratulation is from the mid-15th century.
 
The interjection, “Congratulations!”, an exclamation conveying a sentiment of congratulation, is from the 1630s.
 
In brief, when we congratulate someone, we wish them well, we wish them joy.
 
Reference: Online Etymological Dictionary, https://www.etymonline.com/