Waw is the Hebrew letter that the next eight verses start with. Very few Hebrew words start with this letter, but it is often used as a conjunction as "and". The theme of this section is trust in God.
Psalm 119.41Let your steadfast love come to me, O Lord, your salvation according to your promise;
Again David prays to Jehovah, the Lord, the Eternal I Am. He prays for two things, mercy and salvation. They are in some ways synonymous words in this context, because they are all about the same. When God shows mercy, we share in His salvation.
It is the Hebrew word hesed which in this verse is translated with mercy. This is one of the core words of the Old Testament where it is used 246 times. In old translations hesed was often translated as mercy, but in newer translations it is more often translated as faithful love.
The Hebrew word hesed has a strong relational aspect to it, which we must take with us to understand the word. It's about loyalty and faithfulness between friends. The word is often used about people's attitudes and behavior towards one another, but still more often the word depicts God's attitude and blessings toward the faithful in the covenant people of Israel. God shows hesed - faithful love - toward those He has made a covenant with. It is the covenant relationship that is the origin of God's mercy toward his people.
Mercy, kindness, loyalty, faithfulness and love depict the essence of a covenant relationship and show the content of a covenant life. Hesed is faithful love between people who are in covenant with each other. Because of the pact, they show mercy and are good, merciful, and faithful to one another. It is also worth to note that the Hebrew word hasidim, which comes from hesed and means those who show hesed - faithful love, in our Bibles is translated "the pious, the faithful, the covenant keepers".
When David prays for mercy to come to him, it is because he knows that God in his faithful love sets his people free from adversities and enemies. It is God's mercy, kindness and gracious acts that save us and keep us alive, in spite all our faults and defeats.
Notice that when David asks for mercy, he points to God's promises: "as you have said"! It was what God had said that gave him the courage to pray. He trusts the word of God and points to what God has promised. It is wonderful to be able to come before God and remind him of what he has said. He is a faithful God who watches over His word to perform it.
"May your gentle and faithful love overwhelm me, Lord, for you are my savior and you succeed in what you have promised!"