Pentecost is a time for celebrating the gospel given at Mt. Sinai and the Spirit given after the resurrection of the Christ. The good news at Sinai was that God was going to be with us. He gave His Law as part of the preparation. The Spirit accompanies His Law because the Law is truth. God is indeed with us in Truth. Let us celebrate the reversal of the banishment from His presence with His Spirit in a heart of flesh walking in His statutes, keeping His rules, and obeying them.
Your righteousness is righteous forever, and your law is true. (Psalm 119:142, ESV)
And I will ask the Father, and he will give you another Helper, to be with you forever, even the Spirit of truth, whom the world cannot receive, because it neither sees him nor knows him. You know him, for he dwells with you and will be in you. (John 14:16–17, ESV)
And I will give them one heart, and a new spirit I will put within them. I will remove the heart of stone from their flesh and give them a heart of flesh, that they may walk in my statutes and keep my rules and obey them. And they shall be my people, and I will be their God. (Ezekiel 11:19–20, ESV)