Charles H. Spurgeon wrote, "The whole burden of our salvation rests upon the faithfulness of our covenant God. The whole matter of salvation is centered on the attribute of God's great faithfulness."
Believe God's promises according to the everlasting covenant (Hebrews 13:20-21). God's covenant promises are for every believer (Hebrews 8:10-13). He is faithful to keep his covenant promises. God has bound himself to his people forever with his oath of covenant promises.
Believe God's promises for you in the gospel. Jesus died on the cross as the everlasting covenant sacrifice. God is faithful to forgive and cleanse you from all sin, through the blood of Jesus (1 John 1:7-9). The power of God's covenant promises are proven forever through the resurrection of the Lord Jesus Christ.
Believe all God's promises in Christ. They are Yes and Amen for you (2 Corinthians 1:20). God will not break his covenant word. He has sworn with an oath. Your faith stands upon God's covenant promises. That's God's oath of promise. To doubt God's word in the Bible is to doubt his great faithfulness.
Believe God's promises found in your Bible. That's the assurance of your salvation based upon God's covenant promises. Your assurance is faith in the resurrection of our Lord Jesus Christ, as your covenant surety (Hebrews 7:20-22). God's covenant promises makes your salvation sure in Christ.