Shalom Aleichem: A Sign
We might feel that we are not deserving of having angels escorting us. Those who are meticulous with the Mitsvah of Tefillin all day have a different status that those who aren’t. “And all the
people of the earth will see that God’s Name is called upon you”, this is a reference to the Tefilin one wears on the head (Brachot 6). The power of Tefillin causes angels to be constantly with someone who wears them with proper awareness.
On Shabbat, one does not put on Tefillin, since the Shabbat itself is a sign between God and Israel. Therefore, the merit associated with Tefillin is inherent to the Shabbat.
This means that one may be worthy of being accompanied by angels which is why we recite Shalom Aleichem. (Siddur Olat Reiyah).
It takes incredible awareness to be able to wear Tefillin all day. In order for us to internalize the power of Shabbat as an eternal sign between the Creator and us, it also takes incredible awareness.
When we sing Shalom Aleichem, we must appreciate the tremendous merit involved in having angels escorting us into our homes. We are ready to live every minute of this Shabbos as an expression of this sign.