D&C 41

The Savior gives a stern warning to the saints that at one time or another have sincerely professed his name, which I believe whether in testimony or covenant -

"Hearken and hear, O ye my people, saith the Lord and your God, ye whom I delight to bless with the greatest of all blessings, ye that hear me; and ye that hear me not will I curse, that have professed my name, with the heaviest of all cursings."  (Doctrine and Covenants 41:1)

I consider that serious.