A summing up of God’s work of individual reconciliation.
For by grace you have been saved through faith, and that not of yourselves; it is the gift of God, not of works, lest anyone should boast. For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand that we should walk in them. Ephesians 2:8-10
For by grace you have been saved: Paul cannot speak of this glorious work God does without reminding us that it is a gift of grace, given to the undeserving. We are not even saved by our faith (though faith itself is not a work), but by grace through faith.
We can think of water flowing through a hose. The water is the important part, but it is communicated through the hose. The hose does not quench your thirst; the water does. But the hose brings water to the place you can benefit from it.
“The precise form of words here stresses two things. As consistently emphasized by Paul, it is entirely of His grace, His free, undeserved favour to mankind. Then also this salvation is presented as an accomplished fact.” (Foulkes)