The key to happiness in life is to not stay stuck in ‘I…Me…Mine’ (meaning one’s own personal desires or material gains). Dedicate your life to some larger goal, or to the service of others around you. Then you will find that only happiness flows through your life.
The second thing you need to remember at all times is this, ‘There is someone (the Divine) who loves me very dearly, and is taking care of me at all times. He cannot be without me and He is all capable of removing any lack that I have’.
Knowing this too brings such joy in one’s life.

See, when it comes to doing things in life, you cannot possibly go on doing something or the other all your life. Also, you cannot do something which is beyond your capabilities. So all your actions are limited by your capabilities and by time.

What you are doing now, is something you will not be able to do so well, after 20 years from now. So we are dependent on both time and our capabilities.

But when we remember this – that there is a Supreme power which belongs to us so totally, which is capable of fulfilling all our needs and wishes, and which is with us at all times – then this strong faith alone can keep us happy at all times.
It does not matter what you call this Supreme power, whether you call it the Guru Shakti, or the Paramatma (supreme soul or Consciousness), or God. When you have this faith in you, then you can be happy at all times; regardless of your capabilities. Then you will not feel weak and insecure in your old age also because you know that there is someone who is all-powerful who is taking care of you and protecting you at all times.
So just having this faith alone can make us so happy.

The strength we get from such a faith makes us glow with happiness, and our face lights up with a smile that never fades. This is why Spirituality is very essential in life.