"You see, at just the right time, when we were still powerless, Christ died for the ungodly. Very rarely will anyone die for a righteous man, though for a good man someone might possibly dare to die. But God demonstrates his own love for us in this: While we were still sinners, Christ died for us." Romans 5:6-8

While we were still sinners, Christ died for us. Through Christ, our sins could be forgivened and unrighteousness purified. What is better than this?
What could I do in return? Some church slogans say, "Follow Christ!", but I am not going to die for others and purify anyone with my blood; I dont have that authority! But just as He bled for me when I still didnt know Him, I bled for total strangers, saving lives. Hopefully, the people that my blood saved would have a chance to accept Christ as their personal savior during their extended life time.
Donate blood saves lives.