God, who said,
“Let light shine out of darkness,”
made His light
shine in our hearts.
– II CORINTHIANS 4:6 NIV
The more I read and study God's Word, the more I see spiritual correlations between the Old Testament and the New Testament. Beth Moore spoke of this in Believing God, and it really intrigued me. I used to not want to read the Old Testament because I thought it didn't have anything to do with me. Boy, was I wrong! (I often see myself in the lives of people in the Old Testament. Like the Israelites who were stiff-necked and had to be taught the same lessons over and over. Reminds me so much of myself.) Now when I read the New Testament, I can appreciate it more because of what I learned in the Old Testament.
There are many spiritual applications in the Old Testament--like the 2 Corinthians 4:6 reference. The first one I think of is Hebrews 13:5-6: God has said, "Never will I leave you; never will I forsake you." So we say with confidence,"The Lord is my helper; I will not be afraid. What can man do to me?" I memorized these passages to use during panic attacks. The reference in Hebrews 13:5-6 comes from Deut. 31:6 (Be strong and courageous. Do not be afraid or terrified because of them, for the LORD your God goes with you; he will never leave you nor forsake you.) and Psalm 118:6-7 (The LORD is with me; I will not be afraid. What can man do to me? The LORD is with me; he is my helper.)These are especially good verses to have in your mind when social anxiety tries to kick in.
Paul quotes alot from the Old Testament in his writings. And I believe Isaiah is the most often quoted OT book in the New Testament. Knowing the history that surrounds those quotes makes them that much more meaningful.