A good birth
A good birth is not about physical wealth.It is actually about mental potential and health.
(A)- Imagine you are a rich man
(B)- Imagine you are a dog in a rich man's house
(C)- Imagine you are a Poor man
(D)- Imagine you are a dog in a poor man's house
As you can see option (A) is good,but why
Buddhism has a signature and it is always referring to the path to nirvana.
So the "Good" here is the man in option (A) can easily do many good things when the man in option (C) would have to go through many obstacles in life.
The dogs have no potential so obviously it is a bad birth.
Now consider this
(A)- Imagine you are a rich man, But very unhealthy
(B)- Imagine you are a dog in a rich man's house, But very healthy
(C)- Imagine you are a Poor man, But very healthy
(D)- Imagine you are a dog in a poor man's house, But very unhealthy
The rich man has an issue,He is unhealthy but the poor man is not.So the rich man is fortunate to have wealth but not so fortunate to have health.But the poor man was the exact opposite.
Now consider this
(A)- Imagine you are a rich man, But very stupid
(B)- Imagine you are a dog in a rich man's house
(C)- Imagine you are a Poor man, But very wise
(D)- Imagine you are a dog in a poor man's house
As you can see even though one man is rich he has very low potential to reach nirvana.But the poor man is wise so he is with great potential.This change everything making him the most fortunate,the best birth among these four.
Now consider this
(A)- A god.
(B)- A human.
(C)- An animal.
An animal has no potential towards nirvana.But a man has much,therefore he is more fortunate and his life is good compared to the animals life.
But when you compare a god with a human you see that the god has much more potential than a human.So in this pair the god is the lucky one.
A good Karma
A good karma is something you do which would effect positively in this life or many lives to come.These could give you a birth with much potential to reach nirvana and make you healthy,strong,kind,wise and etc.It could also be powerful enough to give you a birth in higher realms,making it easier for you to reach nirvana.
So any karma that would ease your path to nirvana is a good karma,any birth that would give you a better chance to reach your path to nirvana is a good life / birth.
May triple gems bless you!