The maven package goal and the spring-boot:repackage goal are different in nature. The spring-boot repackage goal is mainly intended to make a JAR or WAR executable from the command line itself using java -jar *.jar while the maven package goal take the compiled code and package it in its distributable format, such as a JAR.It is the spring-boot repackage goal that repackages the JAR produced by maven to specify the main class and make it executable using an embedded container.

Maven Package

• The first, and most common way, to set the packaging for your project via the equally named POM element . Some of the valid packaging values are jar, war, ear and pom. If no packaging value has been specified, it will default to jar.

• When a package is defined,each packaging contains a list of goals to bind to a particular phase ,the jar packaging will bind the following goals to build phases of the default lifecycle : process-resources,compile,process-test-resources,test-compile,test,package,install,deploy.

Spring-boot:repackage

Plugin to be included is :

<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <version>2.1.4.RELEASE</version>
            <executions>
                <execution>
                    <goals>
                        <goal>repackage</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

The configuration repackages a jar or war that is built during the package phase of the Maven lifecycle.

So,Once spring-boot-maven-plugin has been included in your pom.xml, it automatically tries to rewrite archives to make them executable by using the spring-boot:repackage goal. You should configure your project to build a jar or war (as appropriate) by using the usual packaging element.

Reference : https://docs.spring.io/spring-boot/docs/current/reference/html/build-tool-plugins-maven-plugin.html

Spring repackage a jar or war that is built during the package phase of the Maven lifecycle. The following example shows both the repackaged jar, as well as the original jar, in the target directory:

$ mvn package
$ ls target/*.jar
target/myproject-1.0.0.jar target/myproject-1.0.0.jar.original

If you don’t include the configuration, you can run the plugin on its own (but only if the package goal is used as well). For example:

$ mvn package spring-boot:repackage
$ ls target/*.jar
target/myproject-1.0.0.jar target/myproject-1.0.0.jar.original

See more details from spring website using the link

mvn package creates a jar or war.

The spring boot plugin takes that jar or war and repackages them to make them executable from the command line (i.e. no app server needed).

From the plugin docs:

"Repackages existing JAR and WAR archives so that they can be executed from the command line using java -jar."