When writing an essay, once you have mastered the structure in one paragraph, it is achievable in all paragraphs and all essays. But mastering that first paragraph is not easy. Often students over complicate the structure or try to cram too much into one paragraph. Keep it simple!
Here is a snapshot of an introduction that really works – it answers the question (Aquinas/ successful), it shows evidence of wider reading (dictionary definition), it also shows knowledge (Aquinas quote/natural law)- it captures and holds your attention as a reader. But is also quite sophisticated, for example: the quote and the definition are linked together.