As Father so clearly stated in his homily last Sunday, keeping the fast and abstinence is not obligatory. Failing to keep the fast and abstinence is no sin. But! Should we keep the fast and abstinence? Absolutely! (unless there is a very good--i.e., health, etc.--reason not to.)
Sacred Scripture gives us some pretty good incentives to deny ourselves once in a while:
In Luke chapter 13 Our Lord says twice, "No, I say to you: but unless you shall do penance, you shall all likewise perish."
Matthew 17:17-20: And Jesus rebuked him, and the devil went out of him, and the child was cured from that hour. Then came the disciples to Jesus secretly, and said: Why could not we cast him out? Jesus said to them: Because of your unbelief. For, amen I say to you, if you have faith as a grain of mustard seed, you shall say to this mountain: Remove from hence hither, and it shall remove: and nothing shall be impossible to you. But this kind is not cast out but by prayer and fasting.
Specifically, the Ember Days this week are today, Friday and Saturday. Wednesday and Saturday are days of fast and partial abstinence, Friday is fast and (complete) abstinence.
For further reading, Fish Eaters website gives some good information on the Ember Days, as well as guidelines for fasting and abstinence.
God bless you!