Systematic theology can be helpful as you seek to provide a theological context for your sermon text. Here are some resources.
Systematic theologies available online:
Louis Berkhof. Systematic Theology (also here and here) (1941)
Louis Berkhof. Summary of Christian Doctrine (1938)
John Calvin, The Institutes of Christian Religion (1559)
A. A. Hodge. Outlines of Theology (1890)
John Frame. Systematic Theology: An Introduction to Christian Belief (240 page excerpt) (2013)
Wayne Grudem. Systematic Theology: An Introduction to Biblical Doctrine (1994)
Robert L. Reymond. A New Systematic Theology of the Christian Faith (1998)
R. C. Sproul. Essential Truths of the Christian Faith (1992)
Additional systematic theologies:
Herman Bavinck. Reformed Dogmatics: Abridged in One Volume (2011)
Herman Bavinck. Reformed Dogmatics (four volume set) (2008)
John Frame. Salvation Belongs to the Lord: An Introduction to Systematic Theology (2006)
John Frame. Systematic Theology: An Introduction to Christian Belief (2013)
John Frame. The Doctrine of the Word of God: A Theology of Lordship (2010)
John Frame. The Doctrine of God: A Theology of Lordship (2002)
John Frame. The Doctrine of the Knowledge of God: A Theology of Lordship (1987)
John Frame. The Doctrine of the Christian Life: A Theology of Lordship (2008)
Articles on systematic theology:
Kevin DeYoung. “Why Should We Study Systematic Theology?”
Donald MacLeod. “Biblical Versus Systematic Theology?”
B. B. Warfield, “The Practical Importance of Systematic Theology”
B. B. Warfield, “The Task and Method of Systematic Theology”
Audio lectures by Wayne Grudem on systematic theology are available here.
Bruce Ware has an online course entitled, “The Essentials of Systematic Theology.”