For life to have been a gift there would have to be a giver, conscious of what it is giving, and I can't for the life of me consider abiogenesis in such a light.
As far as 'obligation' is concerned, I don't think we are obliged to make the best of life, but I feel that to do so is the most intelligent course to take. The life we have is that of a member of a social species, so antisocial behaviour is a no-no for the majority of us.
But as has already been observed, it is up to each of us how we live our lives.