"This is the covenant I will make with the house of Israel after that time, declares the Lord. I will put my laws in their minds and write them on their hearts. I will be their God and they will be my people." Hebrews 8:10
As soon as you open a Bible, you see that it has two main parts. The two parts are the Old Testament and the New Testament. Even so, a single word describes both of the parts. It is the tremendous word, testament. This word comes from the Latin word, testari. Testari means to testify, and especially ones final testimony, that is, his will.
We still speak of one's final will and testament. A will states a person's wishes about what will happen to their property after they die. Jesus died. But by his perfect life, death, and resurrection, he earned the approval of God the Father. By faith in him, we are made heirs of what Jesus earned. Jesus' will and testament is the gift of eternal life to all who believe in him.
In the Bible, the word testament is the same as the word covenant. God has chosen to "make a deal" with us. This "deal" was born out of God's amazing grace, so it is called the Covenant of Grace." The "bottom line" is given as God sovereignly says, "I will be their God and they will be my people." That is great news! He is our God, our Father, our Friend, our Refuge, our Home, and Source of everything we need to live for him and glorify him.
Speaking of God's grace, Patti Gell, Bible study leader at Evergreen Commons in Holland once said, "Gratitude answers grace like an echo in a canyon."
God's grace elicits gratitude. Gratitude produces obedience to God's law as noted also in the third part of the Heidelberg Catechism. His law is summarized in loving him with heart, soul, mind, and strength and loving our neighbor as ourselves.