Some questions are so vast topic in Hinduism and may have more than one answers. So it should be allowed to accept more than one answer.
Only one answer should be allowed to be accepted. Usually OP selects the best answer among all and as the superlative suggests "best" cannot be many!
Also, giving of +15 reputation with an acceptance, easily may create bloating of reputations. Because there is no minimum reputation requirement to accept an answer (upvote=15, downvote=125).
BTW, if user changes mind, then that answer can be "un-accepted" -- by re-clicking the right tick mark OR by accepting another answer.
Similar post in main meta:
Accept Multiple Answers or Split Bounty among Several Users