20: Who verily was foreordained before the foundation of the world, but was manifest in these last times for you,
21: Who by him do believe in God, that raised him up from the dead, and gave him glory; that your faith and hope might be in God
So who was the 'who' in verse 20? This 'who' was chosen to appear in the end days to deliver us from this world. Through this person's sacrifice, we now have a pathway to God. We are able to speak to God directly through this person, and through this person we are saved. This person was resurrected and brought up to heaven, as proof to us all that God still watches over us, and will not forget us.
This 'who' is Jesus Christ. The perfect man, God's own son.
Because God loves us enough to sacrifice His own son for us;
because Jesus loves us enough to go through so much pain and even be isolated from God;
because men are still ignorant in their sins and bear hatred for one another;
because of these, we christians should be the ones leading by example, showing kindness to friend and foe alike, abhoring sin and striving to be true christian testimonies.