The covenant was with God.
the hebrews
It was because of the Hebrews' covenant with Him that God did the Exodus for them (brought them out of Egypt). This is explicitly stated in Exodus ch.3.
They were getting killed
The Hebrews felt they had a covenant with God. Hebrews 8:10 "This is the covenant I will establish with the people 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"
The land of Israel.
the covenant
Moses
Jesus Christ fulfills the covenant that God made with humanity. Acts 3:25 says "Ye are the children of the prophets, and of the covenant which God made with our fathers, saying unto Abraham, And in thy seed shall all the kindreds of the earth be blessed." The seed of Abraham is Jesus. Galatians 3:17 says that the covenant was confirmed before God in Christ. Hebrews Chapter 8 says a lot about God's covenant. Hebrews 12:24 says that Jesus is the mediator of the new covenant. Hebrews 13:20 mentions the covenant.
The ark of the covenant is important to the Hebrews because it symbolizes the presence of God among them and serves as a connection between God and his people. It contains the tablets of the Ten Commandments and represents the covenant made between God and the Israelites. Additionally, the ark is associated with miracles and divine protection in Hebrew scripture.
Allow me to refer you to the New Testament epistle to the Hebrews. It addresses this very question, especially chapters 7-9.
A covenant is an agreement, compact or contract between two or more parties. God defines all of the conditions. The people could only accept or decline God's offer. Most Hebrews followed it no matter their life is threaten. They believe in the ten commandments and the law of Moises.
In the Old Testament, the covenant between Yahweh and His people Israel (the Hebrews) progressed through multiple stages, and at least two signs were attached to it. When God called Abraham and established a covenant with Abraham and his descendants, He appointed circumcision as the sign of the covenant: "You shall be circumcised in the flesh of your foreskins, and it shall be the sign of the covenant between me and you" (Genesis 17:11 ESV). Circumcision is the most prominent "sign" of the covenant between God and the Hebrews. However, at Mount Sinai, God also established the Sabbath as a sign or token of His covenant with Israel; see Exodus 31:12-18 and Ezekiel 20:11-20. (Earlier on, the rainbow had functioned as the sign of God's covenant with Noah and his family; see Gen. 9:17.)