The concluding sentence may have different functions. The one you choose will depend on the effect you want to produce in your reader. Here are some functions:
Restatement of the main idea: as mentioned in our entry about the topic sentence, this is the one that states the main idea of the paragraph. Therefore, one option to conclude your paragraph is to restate what you said in your topic sentence. For example, if your topic sentence is “At some point, most parents have to decide whether or not to allow their children to have pets”, your concluding sentence could be “In brief, although many children want a pet, parents are divided on this issue for a number of reasons”. If you see both sentences, they refer to the same idea, and there is a logical connection between them. It is a sort of paraphrasing.
Giving an opinion: another good way to finish your paragraph is to provide your own opinion as the writer of that piece of text. For example, if your paragraph talks about the features of sports cars, you could close your it saying “Whatever the reasons, I think sports cars are here to stay”. For this type of sentence, use verbs such as think, believe, consider, regard, etc.
Making a prediction: you can also make a prediction based on your supporting sentences to finish your paragraph. For example, if your paragraph explains different tips to lose weight, your concluding sentence could be something like “By doing all these things, you can be certain that you will lose weight very quickly”.
Offering a suggestion: as a writer, you can also offer a suggestion based on what you wrote. For this, you can use some verbs like suggest, recommend, propose, advise, etc. For example, if your paragraph talks about the advantages of travelling, your concluding sentence could be “Considering all the benefits of travelling, I strongly recommend you leave home and start exploring the world!”.