Because the Lord will supply them the Spirit through your prayers.
A geek with his greek tells me, you’d do well to translate it:
“Your prayers supply the Spirit of Jesus Christ.”
Numerous other places in the Scriptures we can find this truth. The key is what we do with it.
The “‘can I pray for you?’ If yes, hand on the shoulder, ‘Come, Holy Spirit’ then stay attentive” mode of operation really is so powerful, because the Spirit is delighted to honour it.
Disciple, part of our walk is praying for the Spirit to be supplied to others.