Grace is the "finished", "completed",work of Christ on Calvary. Nothing can be added to it or replace it!
Faith, or the corresponding verb pisteuo, is a response to the call of the Father.
So you have the call of the Father to Christ. You have the first response to the call by what is called repentance. Repentance is simply a turning in our minds from our way, to the way of the caller. Then the second response, our first act of Faith or what the Greek calls "Pisteuo".
So were called, we turn, then we take our first step towards God in faith, which is a decision to turn our life and will over to God and Living a life inspired by such surrender every day.
This first step of Faith towards God is done without the Spirit of Christ, and doesn't result in recieving the Spirit of Christ. This is only the start of the salvation journey.
By Grace, through Faith. Grace is the free gift! Through Faith is something We must fulfill as defined in the Vines Greek dictionary. A surrender!