its not necessary (as most things), but it will have an effect on your playing. Not really a bad thing. But the blues elements will shine more. Its kinda like how folks that start in classical and then play gospel will sound different than the guys who start in jazz or rock or even blues. But they still play gospel.
Maybe your teacher feels that since gospel originated from blues to attack it at the source, which is not a bad methodology, but if YOU want your sound to reflect jazz, then you should learn jazz first. That just makes sense.
But does he mean learn to play the blues first or STUDY blues? I think its a difference. With just playing, you dont have to go into much depth, which wont take much from you. I learned funk on bass before i really got into gospel, simply because my instructors were funk players. I learned it, but I didnt get too deep into it, but it reflects a bit in my playing, and I actually notice where it comes out in other players, making the gospel songs they play easier to pick up.
I think the thought is that blues may make LEARNING gospel easier since a lot of it is derived from it. Which is true. Coming from a jazz background, there's still a learning curve to gospel because its different, but once you get it, you can add the jazz elements. I think the thought is, its a different approach in not knowing gospel vs. not knowing how to play at all. So it may be based on your level.
