I've never really liked this statement, as it always seemed so pessimistic and world denying, but listening to a lecture today by Jordan Peterson on "the necessity of virtue" he made some points which stood out for me because they resonate with the Tantric philosophy that says that the absolute willingly limits itself in order to manifest and play out the game of existence. Suffering means dissatisfaction, impermanence, imperfection and most importantly limitation.
"Human 'being' is predicted on a fundamental limitation, in that we are what we are and not other things. That means, inevitably, the awareness of human 'being' comes along with suffering. Thus, life poses the question to us - "how to conduct yourself in the face of suffering", not only yours but everyone else's. It's an inescapable question. If you think about this you might think it's pessimistic, but it's not, it's actually one of the most freeing things you can realize. Maybe there's nothing particularly wrong with you at the moment but there's a high probability that you have a family member that has something seriously wrong with them and there's also a very high probability that if you don't you will soon, and to know this frees you from the false illusion that life can be conducted without suffering. Suffering is an integral part of being.
If we take a being with the classical attributes of God - omnipotence, omnipresence and omniscience - and you ask what does a being with those attributes lack ? The answer is limitation. Without limitation it is all just undifferentiated oneness, there is no 'being' (manifestation) and so to 'be' automatically implies limitation which in turn implies suffering." - Jordan Peterson
Suffering makes people question the validity of life - is it worth it? The process of asking and answering that question underlies everything you do, all of the time. You either act in a way which validates 'being' or negates it. Of course life is not only suffering, there is also joy and beauty, but these conditions fluctuate. The message that "life is suffering" is intended to spur seekers on, to find that which underlies all that is transitory and from the Tantric perspective, this is not meant to be used as an 'escape' but as a transfiguration of the world and oneself such that one is able to experience unity in diversity.