The stunning Christian answer [to the question, “How can a person be right with God?”] is: sola fide—faith alone. But be sure you hear this carefully and precisely: He says right with God by faith alone, not attain heaven by faith alone. There are other conditions for attaining heaven, but no others for entering a right relationship to God. In fact, one must already be in a right relationship with God by faith alone in order to meet the other conditions.
The main problem, as I see it, is that Piper is using confusing and non-standard language, and this leads to lack of clarity.
The first confusing terminology is his language of “entering a right relationship with God.” From the context, Piper seems to be using this phrase as a gloss for “justification.” But as a gloss for justification it is not very helpful. It leads to confusion and mixing things with justification that are distinct from it. Justification is simply the forgiveness of sins (negative removal of guilt) and the imputation of Christ’s righteousness (positive reckoning as righteous). Entering into a right relationship with God is not part of it. Entering into a right relationship with God is a consequence of being forgiven and reckoned as righteous. In traditional terminology, we would speak of this right relationship as our adoption as God’s children and reconciliation with God (or peace with God). Justification is a purely forensic verdict in which we are freed from guilt and are reckoned as righteous before God. To be sure, there is a relational dimension to salvation, but it is the result or consequence of justification, not to be confused with justification itself. Paul made that distinction when he wrote, “Having therefore been justified (dikaiōthentes, aorist participle) by faith, we have peace with God” (Rom 5:1).
The second confusing terminology is his use of the word “conditions.” He wants to say that faith is the sole condition of entering into a right relationship with God. But if we replace “entering into a right relationship with God” with “being justified,” then it is not true that faith is the sole condition, since faith is related to justification not as a condition but as a means. Faith has never been viewed as a condition of justification in Reformed theology or in the Reformed confessions. Paul himself never uses the prepositional phrase dia + accusative, “justified because of faith.” Instead he uses dia + genitive or ek + genitive, “justified by faith.” Faith is not the ground of justification, but the means by which we are justified, by which we rest upon Christ and receive the gift of his imputed righteousness. Faith is a purely passive and receptive instrument. It is an open hand that receives the gift. In this it is the exclusive means or instrument by which we are justified, since we do not receive the righteousness of Christ by works of obedience, even by Spirit-wrought works of obedience. And even faith itself is a sovereign gift of God. So it is simply wrong to say that faith is the condition of justification.
Those whom God effectually calleth, he also freely justifieth: not by infusing righteousness into them, but by pardoning their sins, and by accounting and accepting their persons as righteous; not for anything wrought in them, or done by them, but for Christ's sake alone; nor by imputing faith itself, the act of believing, or any other evangelical obedience to them, as their righteousness; but by imputing the obedience and satisfaction of Christ unto them, they receiving and resting on him and his righteousness, by faith; which faith they have not of themselves, it is the gift of God (The Westminster Confession of Faith [WCF] XI.1).
Piper goes on to say, “There are other conditions for attaining heaven, but no others for entering a right relationship to God. In fact, one must already be in a right relationship with God by faith alone in order to meet the other conditions.”
This is terribly confusing. If we have been justified by faith, we are righteous in God’s sight and therefore entitled to heaven. Christ’s righteousness is sufficient. We do not need to meet any other conditions for attaining heaven. If we have the righteousness of Christ imputed to us, then we are legally righteous in the eyes of God and qualified to attain heaven. “Those whom he justified, he also glorified” (Rom 8:30). If not, then we would be saying that Christ’s righteousness does not merit heaven.
I think what Piper is attempting to say is that faith is the sole instrument of receiving the righteousness of Christ, and if we have true faith, that faith will manifest itself in a changed life as we bring forth fruits of evangelical obedience. If that is what he is trying to say, then I fully agree. The Westminster Confession, again, says it well:
Faith, thus receiving and resting on Christ and his righteousness, is the alone instrument of justification: yet is it not alone in the person justified, but is ever accompanied with all other saving graces, and is no dead faith, but worketh by love (WCF XI.2).
In this sense, it is true to say that no one who enters heaven will be devoid of good works and evangelical obedience. But these things have no role to play as means or conditions of attaining heaven. They are the fruit and evidence of saving faith. We do not attain heaven by means of or on the condition of producing the fruit of faith. We attain heaven by being reckoned as righteous in Christ by faith. But faith is never alone “in the person” who is justified, “but is ever accompanied” with its fruits.
It is important to be precise and clear when explaining the gospel. I am confident that the intent of what Piper wrote is not far from the doctrine as the Westminster Confession articulates it, but I wish he had been more precise and clear in his terminology.