Fair.

Romans 9:15

Exodus 33:17-23

How can I possibly choose between them?

How often do we feel as parents that whatever we give to one child we must also give to another. How many times have we held back from giving something (perhaps the last piece of cake or candy) to any of our children simply because there wasn't enough for all our children to have a portion. Our children take advantage of this feeling that everything needs to be doled out in equal measures and they use it to intensify our feelings of guilt and manipulate us into offering new and more abundant treats. When there is simply no way to make it "fair", even by splitting an item into equal portions, they would rather no one receive the blessing than to see a brother or sister enjoy something without them.
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They're both so precious to me.

God apparently is unmoved by the manipulation that we try to use against Him. When we complain that a sibling received a blessing we were not offered, His answer is simply, "I will have mercy on whom I will have mercy and I will have compassion on whom I will have compassion." And isn't that appropriate? What parent can truly make everything fair anyway? If we give equal portions, aren't we being unfair to the older child in the same way that a single Skittle means nothing to an adult but is a huge bonus to a toddler's diet? That older child should be given a larger portion because he/she is older and bigger. Yet if we give different portions to our different children, aren't we being unfair by always preferring the older child who always gets more simply because his/her birth date precedes that of all the siblings? I certainly wouldn't feel it acceptable to be reduced to things I couldn't control such as my age and size and name, always getting the short-end of the stick with no hope of life being any different, ever.
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When we look at life from this new perspective, there is no need to complain about unfairness in God's Kingdom. We start from a base that is fair, a base that gives us nothing, including no mercy, no compassion, no blessings, no love. Everything beyond that is a gift, which may or may not be handed out in equal portions. So rather than complain that someone has been offered a blessing that was not also offered to us, how much better it would be to rejoice in the above-and-beyond gift that person received and simply thank the Lord that He continues to pour out such abundant treasures on all of us, unfairly.