By Metropolitan Anthony Bloom of Sourozh
Our modern translation 'have mercy' is a limited and insufficient one. The Greek word which we find in the gospel and in the early liturgies is eleison. Eleison is of the same root as elaion, which means olive tree and the oil from it. If we look up the Old and New Testament in search of the passages connected with this basic idea, we will find it described in a variety of parables and events which allow us to form a complete idea of the meaning of the word. We find the image of the olive tree in Genesis. After the flood Noah sends birds, one after the other, to find out whether there is any dry land or not, and one of them, a dove - and it is significant that it is a dove - brings back a small twig of olive. This twig conveys to Noah and to all with him in the ark the news that the wrath of God has ceased, that God is now offering man a fresh opportunity. All those who are in the ark will be able to settle again on firm ground and make an attempt to live, and never more perhaps, if they can help it, undergo the wrath of God.
In the New Testament, in the Parable of the Good Samaritan, olive oil is poured to soothe and to heal. In the anointing of kings and priests in the OT, it is again oil that is poured on the head as an image of the grace of God that comes down and flows on them (Ps 133:2) giving them new power to fulfill what is beyond human capabilities. The king is to stand on the threshold, between the will of men and the will of God, and he is called to lead his people to the fulfillment of God's will; the priest also stands on that threshold, to proclaim the will of God and to do even more: to act for God, to pronounce God's decrees and to apply God's decision.
The oil speaks first of all of the end of the wrath of God, of the peace which God offers to the people who have offended Him; further it speaks of God healing us in order that we should be able to live and become what we are called to be; and as He knows that we are not capable with our own strength of fulfilling either His will or the laws of our own created nature, He pours His grace abundantly on us (Rom 5:20). He gives us power to do what we could not otherwise do.
The words milost and pomiluy in Slavonic have the same root as those which express tenderness, endearing, and when we use the words elieson, 'have mercy on us', pomiluy, we are not just asking God to save us from His wrath - we are asking for love.
From Living Prayer.