Reddit mentions of Gospel Piano: Hal Leonard Keyboard Style Series

If you are confronted by a mode, run away. Learn the way the greats actually learned back in the day:

https://www.youtube.com/channel/UCDdKVro-7hS8cMjBrcqaAMQ/videos?view=0&sort=da&flow=grid

Unless you only care about post "kind of blue" Jazz, Levine's Jazz theory is a detrimental distraction:

http://www.mtosmt.org/issues/mto.00.6.1/mto.00.6.1.rawlins.html?q=mto/issues/mto.00.6.1/mto.00.6.1.rawlins.html

It's hard to imagine a work which thrown so much real jazz and so many great players under the bus.

This looks alot less harmful:

https://www.amazon.com/Jazzology-Encyclopedia-Jazz-Theory-Musicians/dp/0634086782

poor guy still needs modes though. My favorite theory book, which since you know piano, might be interesting. It's a great supplement to Barry Harris Jazz theory.

https://www.amazon.com/gp/product/1423412494/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

I turned 21 a few months ago and my advice is to learn theory/harmony, practice your instrument, and listen to music as much as possible. I play guitar and piano but I didn't know any theory until I first took AP Music Theory as a senior in high school. That class was all classical music, but then I started taking jazz piano lessons and then took a semester at Berklee college of music for a summer which really helped me with all this stuff. Now I'm currently at the University of Texas at Austin and took their jazz theory classes here. If you ever get the opportunity to take a class, then go for it. Get a private teacher if you can as well. With that being said, you don't need to take classes but it definitely helps keep you on track. There are lots of musicians who have had formal training and there are lots that haven't. As long as you learn the information somehow then that's fine. What's important is the actual music and it doesn't matter where you get the knowledge from.

Lido's harmony comes mostly from gospel, soul, and R&B, so listen to a lot of that. Lido said he went to a music high school and that his dad is a gospel choir director in Norway. So he definitely learned a lot from both of those experiences. There aren't many classes that teach the theory behind gospel, soul, and R&B, but there are infinite sources that teach jazz. While they are different, they share a lot of the same qualities. There's so much out there on the internet that's it's become really easy to learn anything.

If you want to get good fast you need to be submerged in music 24/7 and practice efficiently. Surround yourself by people that know music. Listen to a lot of chord heavy music such as Bill Evans, Joni Mitchell, James Taylor, Babyface, Quincy Jones, Chick Corea, Herbie Hancock, Billy Joel, Marvin Gaye, Stevie Wonder, D'Angelo, Take 6, Steely Dan, Norah Jones, Pat Metheny, and even the Beatles, Beach Boys, the Police etc.

Check out newer musicians like Dirty Loops, Moonchild, and Jacob Collier on YouTube:
https://www.youtube.com/watch?v=nls1HtXQe8E
https://www.youtube.com/watch?v=4OxST7pVcAU
https://www.youtube.com/watch?v=9s1baxrxGHU

PS - this book is pretty close to explaining some theory and devices in black gospel: http://www.amazon.com/gp/product/1423412494?keywords=gospel%20piano&qid=1450130675&ref_=sr_1_1&sr=8-1