This is a brilliant article by Kevin DeYoung on why all of us should love and study systematic theology.
So where should you start? My suggestion would be to start with one of the following books:
Bible Doctrine by Wayne Grudem – much easier to engage with than the book below.
Systematic Theology by Wayne Grudem – I love the fact that Grudem always ends each chapter with a hymn of praise. Theology should always lead to worship and he models this so well for us!