Because if you don't know the meaning of the song that basically consist in words, you don't feel totally thoughts, emotions and feelings of the song. Almost you might not like the song but if you listen to the words you can relive their own meaning of life. But, the melody also has a great influence on the emotional state of man. Sometimes, namely music brings man to life, reminds him of certain things, changes its attitude. But, there are some cases in which the person does not understand the language in which the lyrics are written, so the only way to reflect on the song, to introduce you in the mood , it appears to be the melody, the song itself.
The lyrics are what speak to you, what pulls you. In.. I'm not saying that they're not good songs w/o lyrics.. But whether or not I like a song with lyrics is going to depend on the message and lyrics.. Not saying vocal talent and rhythm aren't also a factor on whether or not I like a song.. Just saying if I don't like the lyrics.. I donor like the song
Though other parts of the music may give the general feeling or tone of a song, i.E., light and happy, or dark and ominous, the whole purpose of lyrics is the message itself. If the lyrics don't provide some form of message then they might as well be either in a language you don't understand or not exist at all. Though the music part of a song may be totally subjective as not all people enjoy the same type, i.E., country, metal etc, many songs have been redone to fit those other tastes.
Though having songs about nothing can become popular, what is sad is when the lyrics are sang in such a manor that it really does not matter what they say. Some songs have so much other sound from the instruments that you can't really hear what they are about, other songs have the lyrics so fast that you can only make out a word here and there. There are also songs that use such poor pronunciations that misunderstanding what is said is common. Personally, I feel that there is no point in making the effort of writing lyrics if few if any actually know what they are.
I think there can be alot of divide on this question, and that can vary with everyone's taste in music. Pop music puts more of an emphasis on melodies and song-structure, where-as the lyrics don't mean all that much; same goes with instrumental jazz and some rock music. But there are songs that put a huge emphasis on lyrical structure, and there are some amazing singer-songwriters out there. In some cases, I think that it some cases it can go hand-in-hand. If a song sounds good and it has stellar lyrics, I certainly will enjoy it. Others are more into the distinct voice, and that can also play a role in some cases, maybe more so with popular hit music.
It may sound weird, but humans often look past what's being said and just listen to the sound. A lot of people don't know how vulgar "Rock you like a hurricane" really is, but they still like the song. A personal experience is a Christmas song my family was listening to. The lyrics were about joy and happiness but the song just really sounded sad. It brought the mood down regardless of the message the artist really wanted to send.
I think the most important part of a song is the melody/notes and the musical part of the song. However I think lyrics are a very important part of music. Meaningful lyrics make a good song even better. It depends on why you listen to music. If you listen to music and what something that speaks to you or conveys meaning, then lyrics would be the most important to you. But if you listen to music for how it sounds then the melody is the most important to you.
Most of my music I listen to is dubstep. And hardly any of the stuff I listen to has ANY words at all. I have, like, a couple japanese ones on my playlist, and one that says "Jump" in the background over and over to keep the beat. That's all.
When I listen to music the things that hook me are rhythmically interesting grooves, unique melodies and the apparent passion conveyed with various composition and performance techniques. Most of the time I don't even listen to the lyrics, the only time I do is when the vocals dominate the track for a short period of time.
I usually enjoy instrumentals or songs with little to no lyrics. I keep up with the beat and not the vocals. I can vary to how you like music, but this is my preference in music. Beats, bass, rhythm, and treble is where I look at, lyrics are usually cliche now a days anyway.
Personnally, I've never really listened to lyrics in a song, when I listen to music, i wan't to... Listen to music! If i want to hear good stories, I will read a book or watch a movie. I actually listen to how the voice sound, the same way I listen to piano for example but I do not listen to the words. I think most people today listen to music for the lyrics and that may be why Classical music(for example) is not really popular anymore and maybe also why a lot of modern popular artists are bad, musically. They put all the emphasis in lyrics and not on the part that actually matter.
But this is my opinion.
The only thing a song needs for it to be a song is singing. A song doesn't necessarily need actual words, it can simply be a sung melody. For example, the link at the bottom of my comment is a song, but the artists don't use words once. Therefore, the most important aspect of a song, the thing that a song needs for it to be a song, is vocal music. The presence or absence of lyrics in a composition doesn't affect whether it's a song or not and therefore, isn't the most important part of a song. https://www.youtube.com/watch?v=jt3oAyK_IG8
Take The Pixies, Nirvana, and many other bands. Their lyrics are meaningless, and yet they are good. If you like idiot pop songs from nowadays, they are meaningless too. The real important thing is melody. The way you say the lyrics. Sing Yesterday from The Beatles in another way than the original version, and you will see that even those meaningfull lyrics are horrible when sang in a certain way.
It's subjective opinion which is the most important because everyone listens to music for different reasons. Personally, I listen to mostly rock (soft, hard, or metal) and many of the songs are about relationships or hardships. If you were to take those same lyrics and place them in a different genre, they wouldn't have the same feel. Disturbed is my absolute favorite band and many of their songs are unrelatable to me, but the way David Draimen sings brings me into the world he created so that I can appreciate it. Overburdened is a song by Disturbed and it's haunting and beautiful, but also about hell being overburdened with sinners. Then there's the fact that, even as an Atheist, I can appreciate good quality christian rock no matter how religious the lyrics are.