在laravel中无法将数据传递给邮件

I don't know what the problem could possibly be, I'm trying to pass data to my email form

Mail::send('emails/register', $a,  function($message) use ($a)
{
$message->from('xxx@xxx.com' , 'xxxx');
$message->to(Input::get('email'), Input::get('username'))->bcc('michael@xxx.com')->subject('Registration Mail');
});

I'm using use($a), the array is

$a = array('msg' => $activate);

And I grab the data with

{{ $a['msg'] }}

But I still get the error

Undefined variable: a

I have found many answers regarding this, including this one:

Laravel 4 Mail not passing data

but I can't find what I do different. Can someone advice?

You should use

{{$msg}}

instead of

{{$a['msg']}}