Let's say you have used the iptables-save command to save your current iptables rules to the /etc/sysconfig/iptables file, like this.

iptables-save > /etc/sysconfig/iptables

The /etc/sysconfig/iptables file will now have something like this.

-A INPUT -i lo -j ACCEPT
-A INPUT -s 192.168.0.0/24 -p tcp -m tcp --dport 22 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
-A INPUT -p icmp -m icmp --icmp-type 8 -j ACCEPT
-A INPUT -j DROP
-A OUTPUT -p tcp -m tcp --sport 22 -m conntrack --ctstate ESTABLISHED -j ACCEPT
COMMIT
# Completed on Mon Sep 21 04:55:18 2020

Now let's say you add a rules to iptables. In this example, a rule is added to allow HTTP on port 80.

iptables -I INPUT -p tcp --dport 80 -j ACCEPT

Now, when you use the list the iptables rules, the rule to allow HTTP on port 80 will be listed.

iptables -L -v
. . .
Chain INPUT (policy ACCEPT)
pkts bytes target  prot  opt  in  out source   destination
0    0     ACCEPT  all   --   lo  any anywhere anywhere
0    0     ACCEPT  tcp   --   any any anywhere anywhere     tcp dpt:http

Chain FORWARD (policy ACCEPT)
pkts bytes target  prot  opt  in out source   destination

Chain ACCEPT (policy ACCEPT)
pkts bytes target  prot  opt  in out source   destination

However, the /etc/sysconfig/iptables file will not include the rule to allow HTTP, since the iptables-save command was not used after adding the rule to allow HTTP. Let's issue the iptables-restore command. 

iptables-restore < /etc/sysconfig/iptables

Now, when listing the rules, the rule to allow HTTP is no longer listed, because we restored iptables from the /etc/sysconfig/iptables file.

iptables -L -v
. . .
Chain INPUT (policy ACCEPT)
pkts bytes target  prot  opt  in  out source   destination
0    0     ACCEPT  all   --   lo  any anywhere anywhere

Chain FORWARD (policy ACCEPT)
pkts bytes target  prot  opt  in out source   destination

Chain ACCEPT (policy ACCEPT)
pkts bytes target  prot  opt  in out source   destination