Mercy and Truth are essential things to God, for they help us to fulfill His will in our walk.
The first mention of "mercy and truth" or "grace and truth" appears when Abraham's servant finds a bride for his beloved son Isaac:
"He said, "Blessed be the LORD, the God of my master Abraham, who has not forsaken His lovingkindness and His truth toward my master; as for me, the LORD has guided me in the way to the house of my master's brothers." (Genesis 24: 27)
Notice that he would not have found the bride without the lovingkindness, i.e. mercy and truth of the LORD.
Here we find not just how God's mercy and truth helps the servant, but gives him knowledge.
The writer of Proverbs emphasizes the necessity of mercy and truth in our lives:
They are the foundation for our heads, wisdom, and they are the guiding life in our hearts.
In fact, we have these two crucial elements in our lives today because of Jesus:
"For the law was given by Moses, but grace and truth came by Jesus Christ." (John 1: 17)
His truth sets us free (John 8: 31-32), and we are saved by His grace (Ephesians 2: 8-9)
Today, Jesus is our Wisdom, as well as our righteousness. sanctification, and redemption (1 Corinthians 1: 30)
What the Israelites lacked in Hosea's time, we have today, because Jesus is our Wisdom because He is our grace and truth.