I've been through this before with a few Lutherans here on this blog. The basic answer of those who participated was that baptism does indeed give saving faith, but that faith needs to be nourished by the Gospel in order to grow and flourish. If not, it will whither and die. I mean no disrespect for my Lutheran friends (the few they are!), but what the Lutheran position appears to be to me is simply another form of synergism, or perhaps simply a different and limited version of prevenient grace without calling it prevenient grace. I don't believe the Lutheran construct (if indeed what I've described accurately is the correct Lutheran construct) is correct. For Lutheranism, at least how it's been described to me, the faith given to infants in baptism is only monergistic in its inception. It ultimately lives or dies by how a person is nourished with the Gospel, and that nourishment appears to be a human work and human tending. In the final analysis, salvation is not monergistic, it's synergistic.
From a Reformed perspective, the word "faith" has deep and nuanced meanings throughout the New Testament. In regard to soteriology, I'm fond of Ephesians 2. There Paul describes the universal plight of humanity by singling out the testimony of the Ephesians. Formerly, like all of humanity, they were dead in their transgressions and sins. But by grace they were saved through faith, and that not of themselves- it is the gift of God. That's the paradigm I find expressed in the Scriptures. I don't see any sort of construct that infants have been given some sort of faith at baptism, simply waiting to be acted upon by their own wills.
Now here's where the CARM discussion comes in. A Lutheran presented me the following argument (here abridged, taken from various CARM posts). He argued that in actuality, the Scriptures teach all men have been given faith, based on Acts 17:31, particularly based on the Greek word "pistis". This word most English translations render assurance or proof in Acts 17:31, but the word most often elsewhere is rendered "faith" throughout the New Testament. Here's how he argued:
"So Scripture says GOD has given faith unto all men that He will judge them through Christ through His resurrection. "Because he hath appointed a day, in the which he will judge the world in righteousness by that man whom he hath ordained; whereof he hath given assurance [pistis, faith] unto all men, in that he hath raised him from the dead." Acts 17:31."
"Well, if Luther's translation is considered then it could be considered Lutheran since he translates pistis, faith, in Acts 17:31 as Glauben. There is a consistent unwarranted bias in the English translations of Acts 17:31. If a person has no trouble with "...has given assurance unto all men..." then there is no reason for that person to have trouble with, "...has given faith unto all men..." since the word being translated is pistis, faith. Have you ever come across Matthew 8:10 translated as, "When Jesus heard it, he marvelled, and said to them that followed, Verily I say unto you, I have not found so great assurance [pistis, faith], no, not in Israel?"
"GOD will judge all men through Christ and He has given faith to all men of that through His resurrection. The body of Christ, the church, brings that faith or assurance to all men, i.e., they Go! baptizing and teaching all men..."
"The faith or assurance is Jesus is the savior of all men. Unfortunately, and mysteriously to me at least, some men just won't have it be so."
"In the two passages cited, Matthew 8:10 and Acts 17:31, the word faith is a noun and it is a direct object. The KJV use of the word assurance to translate pistis in Acts 17:31 is fine because faith and assurance are synonymous. The point of contrasting the translation of the two passages (It could have been a contrast of Acts 17:31 with many other pistis passages.) was to demonstrate an unwarranted translational bias and the mental gymnastics people are going through to support their ideas of Christian faith, or support other doctrines, or maybe only to support the conditioning they've received through that English translation. If a person accepts the word assurance as an accurate translation of pists/faith in Acts 17:31 and the passage makes sense to that person without mentally inserting the article then the meaning doesn't change nor is a mental insertion of the article desirable or warranted when pistis is translated as faith. Some people receive this GOD given faith/assurance, some people reject it, and others are yet to hear of it."
"It is the theological bias of the hoop jumping theologians of glory which leads them to a special pleading in translating pistiv in Acts 17:31 as something other than faith."Response
I did a little poking around with my lexical sources and have come to the following conclusion on Acts 17:31. The meaning of pistis is probably "proof" rather than "faith." While this isn't the most typical meaning of pistis, I see it as the most applicable meaning in context. There are examples of pistis being used as "proof" in relevant extra-biblical Greek sources.
I'm certainly not any sort of Greek scholar, but I certainly don't have any problem consulting Greek scholars. Gerhard Kittel's Theological Dictionary of the New Testament says the phrase in question "has the Gk. sense 'to give a pledge,' 'to offer proof." (Vol. VI, p. 204). See also Mounce, "faith" entry, point 3- "Pistis can refer to an assurance or proof. God has given us assurance that he will send Jesus back to judge the world by raising him from the dead (Acts 17:31)."
31 because He has fixed a day in which He will judge the world in righteousness through a Man whom He has appointed, having furnished proof to all men by raising Him from the dead.”
31 For he has set a day when he will judge the world with justice by the man he has appointed. He has given proof of this to everyone by raising him from the dead.”
I wonder if perhaps those whom Paul was preaching to used the word pistis in regard to proof / assurance? That is, Paul throughout this section uses their capital to preach the gospel. He quotes their poets and philosophers, and appeals even to their idolatry. It would not surprise me at all to learn that that is how the word was being used by Paul's hearers. The concept of the bodily resurrection was seen as ridiculous (Acts 17:18-19). By the end of this section, the very thing those listening to Paul thought was ridiculous is the very proof that God has the right to command all people everywhere to repent.