If you want to make a book, like if you want your book to get picked up by a publisher who will invest money into editing, design, printing and marketing and all that, then you need to have an appealing and strong author voice.
By that, I mean that certain something that shines through the plot, the characters, the description and every other part of your story and comes to rest upon the reader in a pleasing way.
It is much like person to person communication. I can sit down and talk to you and may have something interesting and important to say but if you don't like my tone or my facial expressions or the way I constantly smack my lips while speaking or never make eye contact or talk with my mouth full then it's not likely you'll want to listen to me for very long.
Voice is like that. If it is clear and strong and true it connects with the reader, who will then be more than willing, even eager, to continue this journey of discovery within the pages of the book.
How to get a distinct author voice? There is one way and one way only. It comes with practice. Write write write and write some more.