purchase mine craft account to play error

[crazy jordon]

when i go to play on tekkit and i put my password and username in it a error came up saying you purchase a mine craft acount to play if any body can help i wuold be grateefull thanks :)

[Melfice]

Well, do what it says.

Buy Minecraft.

[crazy jordon]

i have done but it keeps saying it

[Melfice]

And you can play vanilla Minecraft normally?

EDIT: The deafening silence almost tells the whole story, doesn't it?