The Feast of Weeks is the first day of the wheat harvest. On the first day of the barley harvest, the high priest waved a small bundle of barley sheaves as a wave offering to Yah. It was the Firstfruits wave offering. Messiah Yahoshua rose again on the Feast of Firstfruits, and as the new Great High Priest, the Firstfruits wave offering of the barley harvest was the OT saints who had risen again with Him (they were seen walking around Jerusalem—Matthew 27:52-53).
Then for seven Sabbaths (seventh day of the week), the high priest presented a sheaf of barley as an offering each day, and that is what was called the “COUNTING OF THE OMER.” It went on for 49 days. Seven weeks after Firstfruits is the Feast of Weeks. Both feasts are firstfruits celebrations—Firstfruits is the first day of the barley harvest, and Weeks is the first day of the wheat harvest. Both grains are planted at the same time, but barley is harvested seven weeks before wheat.
When Moses led the Israelites out of Egypt (the world) immediately after the angel of death had “passed over” them, the Holy Spirit led them to Mt. Sinai, and once there, they awaited the giving of the physical covenant—the Ten Commandments (which were literally written on stone tablets by the Holy Spirit). They received it seven Sabbaths plus one day from Firstfruits—which is what the Feast of Weeks commemorates.
Messiah was crucified on Passover, and rose again on Firstfruits. 49 days after Firstfruits, ON THE FEAST OF WEEKS, the new covenant (spiritual, rather than the foreshadow—the Ten Commandments, which was physical) was given to Messiah’s bride—and that covenant is the seal of the Holy Spirit (Acts 2). He is what the physical covenant and the written law foreshadowed. That is why those who are led by the Spirit are not under the law, as the law was only the shadow, the Spirit is the real substance.
Now, regarding the COUNTING OF THE OMER, which is the daily offering of a sheaf of barley, the word “OMER” in the Hebrew literally means “PROMISE.” Each day during the 49 days, the PROMISE of Yah’s covenant being given was offered back to Him, in anticipation of the completion of that promise—the giving of the covenant.
In Ephesians 1:13, Paul says, “In Him, you also, after listening to the message of truth, the gospel of your salvation– having also believed, you were sealed in Him with the Holy Spirit of PROMISE.”
Being led to the mountain and receiving the covenant are two different things. Your belief and the giving of the Holy Spirit are two different things. Once one believes, his genuine faith will cause him to offer back to Yah, daily, the promise He made concerning giving His covenant to those who believe, knowing that He will fulfill that promise by sealing the believer with the Holy Spirit.
The Holy Spirit is the OMER, or promise, to the bride, who is the barley! The counting of the omer is the adding of barley to the harvest by the giving of the Holy Spirit to those who believe. Those whose belief in Yahoshua the Messiah has been completed have that evidence within them—the witness (1 John 5:10), and they receive a personal confirmation of that directly from Him.
Salvation BEGINS with Passover (belief), but is completed at Weeks—the giving of the covenant, after the trying of one’s belief (James 1).
For more information: What Are the Old and New Covenants?