passing param using value-of

This works fine.

 <xsl:call-template name="myTemplate">
        <xsl:with-param name="arguments" select="preceding-sibling::*" >
        </xsl:with-param>
</xsl:call-template>

But this doesn't:

<xsl:call-template name="myTemplate">
        <xsl:with-param name="arguments">
             <xsl:value-of select="preceding-sibling::*" />
        </xsl:with-param>
 </xsl:call-template>

Why ? How do I use value-of to set the value of a parameter ?