In Excel, when you pasting text from other application like word, notepad, web browser or any application, the spreadsheet breaks multiple paragraphs into multiple cells. It means also you overwrite existing data under your target cell. To prevent this, simply press F2 or double click the cell the paste. All the text will remain in one cell.
Or, when you type in a cell, you want make new line/multiple paragraph in a cell? First, type the text for the first line/paragraph. To make the new line/paragraph press Alt + Enter. Continue type your next line/paragraph. You can use this trick instead of wrap text for manual breaking of a sentence.