The Atonement is extremely important in biblical theology. If you understand one point of doctrine about the cross, understand the substitutionary atonement. “Soteriology is a doctrinal field that includes things like justification, regeneration, conversion, and sanctification. Soteriology is grounded in the atonement, the objective work of Christ. Christ’s work is grounded in his person, meaning the doctrine of the incarnation . . . presupposes the doctrine of the Trinity.” 
Leon Morris explains the significance,
“To put it bluntly and plainly, if Christ is not my Substitute, I still occupy the place of a condemned sinner. If my sins and my guilt are not transferred to Him, if He did not take them upon Himself, then surely they remain with me. If He did not deal with my sins, I must face their consequences. If my penalty was not borne by Him, it still hangs over me. There is no other possibility. To say that substitution is immoral is to say that redemption is impossible. We must beware of taking up such a disastrous position . . .” 
Here are some recommended resources to help you better understand the cross and Christ’s work there.
- Read Scripture:
- Start in Exodus 12 on the passover lamb.
- Leviticus 16 on the Day of Atonement
- Isaiah 52:13-53
- Hebrews 9-10
- Blog article “Penal Substitution and Church History” by Dr. Michael Vlach
- Book, Pierced for Our Transgressions edited by Jeffery, Ovey, and Sach. This is a great book highlighting a range of topics and issues from exegesis to historical issues.
- The Master’s Seminary Journal volume 20.2 from Fall 2009. This journal covers in depth analysis from both the Old and New Testaments, historical theology analysis, and the relationship between the atonement and worship.
- Blog “The Heart of The Gospel” by Jason Vaughn. A brief article explaining the substitutionary reality of the cross and its relationship to both corporate and individual worship.
- If you are interested in researching other views, The Nature of the Atonement: Four Views, is a good starting place.
- For a great book on all doctrines of salvation (including a chapter on the atonement), see Bruce Demarest, The Cross and Salvation: The Doctrine of Salvation.
What other resources do you recommend?
 Fred Sanders, The Deep Things of God: How the Trinity Changes Everything, 74.
 Leon Morris, The Cross, 410.