[Tex/LaTex] How to justify and preserve the paragraph spacing at the same time

Question

\documentclass[10 pt,a4paper,twoside,reqno]{amsart} 
\usepackage{amsfonts,amssymb,amscd,amsmath,enumerate,verbatim,calc,graphicx} 
\renewcommand{\baselinestretch}{1.2} 
\usepackage{bm}
\usepackage{ragged2e}
\textwidth = 12.5 cm 
\textheight = 20 cm 
\topmargin = 0.5 cm 
\oddsidemargin = 1 cm 
\usepackage[abs]{overpic}
\evensidemargin = 1 cm 
\pagestyle{plain} 
\newcommand\blfootnote[1]{%
\begingroup
\renewcommand\thefootnote{}\footnote{#1}%
\addtocounter{footnote}{-1}%
\endgroup
}
\newtheorem{theorem}{Theorem}
\newtheorem{definition}{Definition}
\begin{document}
\justify
\centering
\title{\textbf{ON THE REFLECTION PROPERTY OF A CIRCULAR PARABOLOID}}
\maketitle
\author{\textbf{S. Aryan}}
\begin{abstract}
 Text for abstract. 
\end{abstract}
\section{Introduction}
\justify
 This is the introduction. 
 \end{document}

When I run this code. I get the text "This is the introduction" printed without the initial space before the word "This." I want the paragraph to be justified but when I use \justify I lose the space before the first word that marks the beginning of a paragraph. Is there a way to resolve this trade-off? In order to make my problem more clearer, I have posted below an image that shows the paragraphs in my actual document.

I want the word "The" in the image to be shifted to the right to mark the beginning of a paragraph.

Answer 1

Edit: After reexamination of your MWE I observe, that your problem is use of \centering and \justify and placing of \author{...}. After removing former two commands and moving latter in correct place (before \maketitle), your MWE become:

\documentclass[10 pt,a4paper,twoside,reqno]{amsart}
\usepackage{amsfonts,amssymb,amscd,amsmath,enumerate,verbatim,calc,graphicx}
\renewcommand{\baselinestretch}{1.2}
\usepackage{bm}
\usepackage{ragged2e}
\textwidth = 12.5 cm
\textheight = 20 cm
\topmargin = 0.5 cm
\oddsidemargin = 1 cm


\usepackage{blindtext}

\begin{document}
\title{\textbf{ON THE REFLECTION PROPERTY OF A CIRCULAR PARABOLOID}}
\author{\textbf{S. Aryan}}
\maketitle

\begin{abstract}
\blindtext
\end{abstract}
\section{Introduction}
\blindtext
\blindtext
\end{document}