I have played bass guitar on and off since I was about 16. My step-father plays and got me hooked on the instrument. When I was single and in college, music was a major part of my life. I ran around with a local band, went to many, many concerts, and bought a new cassette or CD weekly.
My personal practice time was a large part of my daily routine. I had one of the old-style weighted metronomes like you see piano teachers use on TV or the movies. I would set the timing at 60 beats per minute and play scales. I would start at the top of the neck, play the scale forward, then play it in reverse until I came back to the root note. If I muted or missed a note, I would replay that scale until I got it right. Then, I'd move my hand down one fret and play the scale again. I repeated this process until I reached the bottom of the neck. At that point, I began moving back up the neck until I reached the top.
I then moved the metronome speed up one click to 64 BPM and repeated the entire process.
I then moved the metronome speed up one click to 72 BPM and repeated the entire process.
I then moved the metronome speed up one click to 76 BPM and repeated the entire process.
I continued this process until I reached the point at which I could not consistently play the notes properly and accurately.
This training exercise benefited me in three major ways. First, it forced me to work on my technique, so that I played the easy, slow notes with the same precision and skill as the harder, faster notes in a song. Second, the hours and hours of practice put callouses on my fingers that actually helped me play better.
The greatest benefit, however, was that I learned to identify individual notes by simply hearing them. Pick any note on the musical scale, and there are eight different ways to play them on a four string bass, if the neck is fretted to two octaves. An open E string, an E played on the 7th fret of the A string, an E played on the 2nd fret of the D string and an E played on the 9th fret of the G string all have a different feel. They are all the same note, but like shades of a primary color, they are clearly different to someone who spends time interacting with them.
While I don't read music, I could listen to a song on the radio and instantly pick up my bass and play along. I knew the sound of the bass guitar, and could also discern when a certain Canadian bassist was using foot pedals instead of playing his bass so that he could play keyboards with his hands. They sound close, but they are not the same.
Jesus talked about this too. In John 10:27, He says "MY sheep hear MY voice, and I know them, and they follow ME."
A Christian must spend time in prayer and in the Bible developing callouses. Learning to perfect our technique of relying on Christ and His Word as we interact with the world. And above all, learning to know HIS voice. False teachers, ear-ticklers and feel-good profits are everywhere, claiming to speak the Gospel.
We must know the difference, not only for our own benefit, but you cannot accurately point someone else to Jesus, if you are listening to an imitation.