Yo can hear the difference, can't you? When a sermon is full of truth or if it isn't. When a person is sincere and when they aren't. Discernment is a gift given to some on the Body (1 Corinthians 12:10), discernment is also a skill demanded of all (Hebrews 5:14).
The illustration below is an example of how you can hear discernment
There was an old pastor, so old that he had been forced to retire. His voice cracked from years of preaching. He was a humble old gentleman. He was invited to a high society kind of luncheon by a friend. He really was out of his league, frankly, but he went. And there was a famous actor there, and the one who was heading up the luncheon said to that actor in the midst of all of the folderol,
"Oh, would you stand up and recite something for us?" And he said, "Of course, I have an endless repertoire. What would you like?" The old pastor thought this is his moment. He said, "How about the 23rd Psalm" And the actor said, "Well, that’s an unusual request, but I happen to know that, and I’ll do it on one condition: that you'll do it after I do it."
Well, the old pastor hadn’t bargained for that, but for the sake of the Lord he said, "All right." The actor got up, and he recited the 23rd Psalm with great intonation, beautiful, lyrical voice, tremendous interpretation. And he finished, and everyone applauded. The old pastor stood up and cracking voice and just went through the 23rd Psalm in his humble way. And when he was done, there was not a dry eye in the room.
And sensing the emotion of the moment, the actor stood and said, "I think I understand the difference in your response to me and to him. You clapped for me; you wept for him. The difference is: I know the Psalm, but he knows the Shepherd." ~John MacArthur, The Calling of the Church
And that IS the difference when you hear it. Some recite from the mind, others know from the heart. A worthless shepherd who doesn't know the Shepherd will be empty, though he deliver his words confidently, or with flair, or eloquently. Lord, give us ears to hear. See Revelation 2:7, "He that has an ear, let him hear what the Spirit said to the churches;"
He that hath an ear—This clause precedes the promise in the first three addresses, succeeds it in the last four. Thus the promises are enclosed on both sides with the precept urging the deepest attention as to the most momentous truths. Every man "hath an ear" naturally, but he alone will be able to hear spiritually to whom God has given "the hearing ear"; whose "ear God hath wakened" and "opened." (Jamieson-Fausset-Brown Bible Commentary)
Discernment is something we can ask for more of (Psalm 119:66). It is something you can pray for others to be given it (Philippians 1:9). What a privilege to be able to ask the Wise one for more wisdom and discernment.