Matthew 5:7
What does it mean to have mercy? Is it just another word for compassion, or something more?
Both have an element of forgiveness in them, yet I believe that in general humans show compassion easier than mercy. Compassion heavily involves the emotions of the heart. If we feel sorry for, love, or are able to empathize with someone, we tend to forgive them and do nice things for them without much effort. Mercy on the other hand, is still an attitude of the heart, but is rooted in obedience and love for God. In other words, you can have mercy on someone you don't care for at all because you care so much for God.
Now, the tricky thing about mercy is that just because we portray it, doesn't mean we have it. Proverbs 12:10 says, "A righteous man cares about his animal's health, but even the merciful acts of the wicked are cruel." Though the wicked man showed what he considered to be mercy out of obedience to law, or whatever ruled him, but it was still considered to be cruel. His mercy was rooted in obedience, yet not at all in love.
So how does that work concerning the mercy we will receive? Some of it between humans is that old cliché "What goes around, comes around." God however, will show us mercy instead of justice, when we show mercy to others. The law He is obeying is His own.
"Let your eyes be turned to me, and have mercy on me, as it is right for you to do to those who are lovers of your name." Psalms 119:132 (BBE)
"...For I, the LORD your God, am a jealous God, visiting the iniquity of the fathers upon the children to the third and fourth generations of those who hate Me, but showing mercy to thousands, to those who love Me and keep My commandments." Exodus 20:5b-6 (NKJV)
We will receive mercy when we show mercy, and one of the blessings we will receive from the Lord is His faithful and loving mercy while still in this life. Why? Paul says it best...
"But I received mercy because of this, so that in me, the worst of them, Christ Jesus might demonstrate the utmost patience as an example to those who would believe in Him for eternal life." 1 Timothy 1:16