Zadkiel is known as the Archangel of Mercy. He helps people approach God for mercy when they've done something wrong, encouraging them that God cares and will be merciful to them when they confess and repent of their sins, and motivating them to pray.
Zadkiel was also the angel who prevented the prophet Abraham from sacrificing his son, Isaac, when God tested Abraham's faith and then showed mercy on him. Just as Zadkiel encourages people to seek the forgiveness that God offers them, he also encourages people to forgive others who have hurt them, and helps deliver divine power that people can tap into to enable them to choose forgiveness, despite their hurt feelings.
Zadkiel helps heal emotional wounds by comforting people and healing their painful memories. He helps repair broken relationships by motivating estranged people to show mercy to each other. Zadkiel comes in the form of a little girl, since children radiate an innocent and calm aura around them. When Zadkiel approaches someone, it prevents those from panicking upon seeing Zadkiel's true form. So he prefers to come towards someone who begs for mercy in the form of a girl.