While on the surface they seem the same, Motivation and Discipline are very, very different.
Motivation means to "Motivation is the process that initiates, guides, and maintains goal-oriented behaviors. It is what causes you to act, whether it is getting a glass of water to reduce thirst or reading a book to gain knowledge. Motivation involves the biological, emotional, social, and cognitive forces that activate behavior." While motivation is a powerful short-term initiator, it will eventually fade and you will revert to your old habits, and skills.
The word "Discipline" is from the Latin word disciplina meaning "instruction and training". It's derived from the root word discere -- "to learn." ... Discipline is not rules, regulations, or punishment. It is not compliance, obedience, or enforcement. Discipline, to me, means that you apply things that you learn from instruction and training and apply those "disciplines" to your life. It also means that you are actively choosing to behave in a certain way, in order to achieve something. Most disciplines are directed towards making movements that will positively influence your life in the short and long term.
Think about that difference when it comes to meeting your goals. In the case of discipline, this skill or quality, will transfer into other areas of your life when motivation is long gone!