Important to Biblical doctrine and Reformed theology is union with Christ. When a believer trusts in Christ they are united to Him. When they are united to him they receive the benefits that Christ has won. Sometimes union with Christ is downplayed when the various aspects of the union are emphasized. We must think of the one without losing site of the others--we must see the overarching with paying attention to the particulars.
John Flavel says this:
"That Christ and his benefits go inseparably and undividedly together: it is Christ himself who is made all this unto us: we can have no saving benefit separate and apart from the person of Christ: many would willingly receive his privileges, who will not receive his person; but it cannot be; if we will have one, we must take the other too: Yea, we must accept his person first, and then his benefits: as it is in the marriage covenant, so it is here." (Works of John Flavel, Vol 2, p.17)
For Flavel--the Gospel itself entails the application of the gospel to the lives of the believers. God not only accomplishes the gospel but applies it to us by uniting Christ to our souls. So Christ's work is meritorious and the cause of our salvation but note: "neither the one [Christ's humiliation] or the other [Christ's suffering] can actually save any soul, with the Spirit's application of Christ to it;" (Flavel, Works, Vol 2, p.20).
The last application Flavel makes after expounding this doctrine:
"If Christ, with all his benefits, be made ours, by a special application; how contented, thankful, comfortable, and hopeful, should believers be, in every condition which God has cast them into this world!"You can find the first sermon in Flavel's Work here.