Answer:
To disguise himself.
Step-by-step explanation:
Odysseus wore beggars clothes due to not knowing how he would be welcomed. Since he was missing for twenty years, he could not count on anyone to be waiting patiently. He disguised himself to find out it he would be welcomed well.
It only took a little bit for him to figure out that suitors were lined up for Penelope. After he confided in his son, Telemachus, and found himself accepted, Odysseus and his son took care of the suitors.
Then, Penelope and Odysseus reunited.