To expand on the comment by @moewe: you can use the enumerate environment to number the lines, which aligns the text automatically. By default the numbers appear as 1., 2. etc. There are several ways to change the appearance of the numbers. An easy way is to use the enumitem package with the option shortlabels as in https://tex.stackexchange.com/a/2294/, and specify the label as [(1)] at the start of your enumerate environment. MWE:
\documentclass[12pt, a4paper]{article}
\usepackage[top=0.7 in,bottom=0.5 in,left=0.6 in,right=0.6 in]{geometry}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{parskip}
\usepackage[shortlabels]{enumitem}
%line spacing
\renewcommand{\baselinestretch}{1.10}
%reduce top margin
\addtolength{\headsep}{-0.45cm}
\begin{document}
\begin{enumerate}[(1)]
\item This is the first line. This is the first line. This is the first line. This is the first line. This is the first line. This is the first line.
\item This is the second line.
\end{enumerate}
\end{document}
Result:

Edit: if you don't want an indent then you can change the leftmargin parameter of the enumerate environment. If you set it to \labelwidth then the margin will be just big enough to allow the number to be printed and the indent is gone. However, the width of the label is slightly bigger than the printed number, so it still looks a little bit misaligned with regular text. This may not necessarily be bad typographically, but if you want you can shift the number further left by manually setting the labelwidth.
MWE:
\blindtext
\begin{enumerate}[(1),leftmargin=\labelwidth]
\item This is the first line. This is the first line. This is the first line. This is the first line. This is the first line. This is the first line.
\item This is the second line.
\end{enumerate}
\begin{enumerate}[(1),labelwidth=7.6mm,leftmargin=\labelwidth]
\item This is the first line. This is the first line. This is the first line. This is the first line. This is the first line. This is the first line.
\item This is the second line.
\end{enumerate}
Result:

\begin{enumerate} \item This is ... \item This is another .... \end{enumerate}for lists. The indentation should be more visually pleasing then. – moewe Mar 07 '19 at 08:50enumitem) if so desired. The question is not so much whether or notenumerategives the exact expected output from the start (it can be configured quite extensively), the question is whether semantically it is the right choice here, i.e. if the OP wants to typeset a numbered list. – moewe Mar 07 '19 at 08:58enumerateusage it may help to explain why you don't want to use it and what exactly you intend on doing here. – moewe Mar 07 '19 at 09:49