We then begin counting the fifty days until the next feast, Shavuot (Pentecost). 

This is called the Counting of the Omer. This count connects the redemption of the cross depicted in the Spring feasts to the giving of the Holy Spirit at Shavuot and is traditionally associated with the giving of the Torah on Mt. Sinai.

The giving of the Holy Spirit thus fulfills the prophetic meaning of the feast. At Shavuot we have a special service and teaching.