This is (almost) a simple cryptogram using numbers rather than
letters to encode the message. It reads:
ONCE YOU HAVE DECIPHERED THIS MESSAGE YOU WILL ALMOST HAVE THE
ANSWER. PUTTING IT TOGETHER IS AS EASY AS ONE TWO THREE.
So go back to 1, 2, 3 in the cipher key, and a bit more:
| 1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
11 |
12 |
13 |
14 |
15 |
16 |
17 |
18 |
19 |
20 |
21 |
22 |
23 |
24 |
25 |
26 |
| D |
E |
C |
O |
D |
I |
N |
G |
U |
L |
A |
R |
W |
S |
V |
M |
H |
T |
P |
Y |
It's not entirely a cryptogram because two letters represent D,
but that was needed to spell the answer this way.