The Canons of Dort say Christ acquired faith for us by His death (Point 2, article 8).1 The significance of this seemly minor point is that Christ buying the condition of the covenant effectively changes the covenant from conditional to unconditional. Christ buying faith links the provision and application of Christ’s blood – ensuring the provision and application are co-extensive.
When the bible says Christ bought us or redeemed us from the curse of the law, being made a curse for us, it’s talking about penal substitution. God’s law and justice demand the punishment of sinners, so we were lawbreakers and under a sentence of death. Christ redeems us by penal substitution – He satisfies justice by His death.
The same cannot be said for faith. The bible never says Christ bought or redeemed faith. Does faith need to be rescued? Is faith a lawbreaker and under a sentence of death? It’s not like the bible speaks of Christ’s death overcoming some obstacle to God giving us faith. Rather, scriptures speak of God redeeming us from sin’s penalty.
1 For a more recent example, see Schrock’s chapter 4 in Whomever He Wills, page 103.