Original:  They sacrifice their entire lives to nurture their relationships. Such a selfless service that his whole life has received from his family deserves something important. That's why National Senior Citizens' Day is celebrated. When they dedicate a special day of the year to the elderly, they give their families the opportunity to see their love and commitment.
Revised:  By dedicating a special day of the year to the elderly, they give their families the opportunity to see their love and commitment.
Edit intent: coherence