Luke 20

The Pharisees understood that priesthood authority comes from God, under His direction and and authorized ministers, thus they asked the Savior -

"...Tell us, by what authority doest thou these things? or who is he that gave thee this authority?"  (New Testament | Luke 20:2)

His answer and outcome was quite interesting -

"...I will also ask you one thing; and answer me:
4 The baptism of John, was it from heaven, or of men?
5 And they reasoned with themselves, saying, If we shall say, From heaven; he will say, Why then believed ye him not?
6 But and if we say, Of men; all the people will stone us: for they be persuaded that John was a prophet.
7 And they answered, that they could not tell whence it was.
8And Jesus said unto them, Neither tell I you by what authority I do these things."  (New Testament | Luke 20:3 - 8)

Obviously, these wicked men were trying to trap him, but they failed.  But we do know that John the Baptist -

"...was ordained by the angel of God at the time he was eight days old unto this power..."  (Doctrine and Covenants | Section 84:28)

Thus priesthood authority comes by ordination.

On a different topic, I love what the Savior taught His disciples -

"Beware of the scribes, which desire to walk in long robes, and love greetings in the markets, and the highest seats in the synagogues, and the chief rooms at feasts;
47 Which devour widows' houses, and for a shew make long prayers: the same shall receive greater damnation."  (New Testament | Luke 20:46 - 47)

Again, the Savior denounces hypocrisy and teaches humility.