While wikipedia can be useful for some things, I would venture to add that Systematic theology is the development of the teaching of Scripture which rests on the conviction that God is consistent in his teaching and actions.

This means that it is possible to gather together all the passages of Scripture on a particular topic and distill the teaching so that the relationship of each of its parts may be seen and appreciated. So, for example, when we look at the teaching of Scripture on murder we discover that God makes a distinction between killing as a judicial act (commanded by God for those who take the life of another) and killing another human being. We also discover that murder is an act which has as its basis a planned determination to put the other person to death - rather than an act where someone is killed either by accident or as an un-premeditated response.

That the killer was to be pursued by the Avenger of Blood and that God made a provision for his life (in case the death was un-premeditated). That the death penalty was to be enforced if premeditation could be proved and that in all other cases the person was to be confined to the City of Refuge till the death of the High Priest.

There are other provisions but these suffice to show how the development of a systematic understanding of the theology of the Bible proceeds. I hope this is of some assistance.