There are ways faith and faithfulness can be contrasted. For example, we are all supposed to be “faithful” to to every single command God has given. We are supposed to love God with all our strength. Anything less is “unfaithful” to our Lord. And we trust in Christ that God will forgive us as we constantly fall short of this fully faithful love. We sin every day (and more) and we trust, have faith, in Christ for forgiveness.

All true.

But it is not the only way that term “faithfulness” is used in the Bible or in historic Christianity of any sort.

I once heard a pastor say that he was an “unfaithful” husband to his wife. Sounds dire to most people. Who was the other woman? Does his wife have the right to divorce him now.

No, nothing so serious.

This man was talking about all the normal ways in which he fell short of the constant unselfish love that he had promised in his wedding vows. He was drawing a parallel between his sinning against his wife and relying on her forgiveness and the way we sin every day against God.

This, I think, was supposed to strike us as a spirit of humility.

Let me ask a couple of questions:

First, what would happen if we turned the tables? Surely this man’s wife, like every wife, fell short on a day to day level in all the obligations of love and submission to her husband. So would it be fine for him to publicly accuse his bride of being an “unfaithful wife.” I’m not asking if it is bad to publicly talk about one’s spouse’s sins. She might get angry about that, but I’m wondering if she might be much more angry believing she was slandered. What does “unfaithful wife” imply about her behavior? She would have every reason to be angry and deny that she had never ever been unfaithful to her lying husband.

Second, why doesn’t his wife have the right to divorce him? If he is an “unfaithful husband,” then that is what she should be able to do. But she would be wrong to divorce him. Why? Because he has never been unfaithful to her.

Now, the people of God are called “the bride of Christ” because they are in covenant with Christ like a wife and husband are in covenant with each other. The Westminster Larger Catechism describes this covenant on the basis of the preface to the Ten Commandments:

Q. 101. What is the preface to the Ten Commandments?
A. The preface to the Ten Commandments is contained in these words, I am the LORD thy God, which have brought thee out of the land of Egypt, out of the house of bondage. Wherein God manifesteth his sovereignty, as being JEHOVAH, the eternal, immutable, and almighty God; having his being in and of himself, and giving being to all his words and works: and that he is a God in covenant, as with Israel of old, so with all his people; who, as he brought them out of their bondage in Egypt, so he delivereth us from our spiritual thraldom; and that therefore we are bound to take him for our God alone, and to keep all his commandments.

Keeping “all his commandments” might sound like it demands a definition of faithfulness that is the same as sinlessness. But the commands that came down from Sinai as explanations and elaborations of the First Commandment don’t work that way:

One of the main original applications of having no other gods but the LORD (1st command) was a demand that one only sacrifice to and worship the LORD. And what was one blessing involved in sacrifice and worship?

So the priest shall make atonement for him for his sin, and he shall be forgiven (Leviticus 4.26).

This promise is repeated many times. Obviously, God did not consider people to be unfaithful to his covenant when they sinned. He promised them forgiveness. God was obligated to forgive them by the terms of the covenant.

Thus Jeremiah prayed:

I know, O LORD, that the way of man is not in himself,
that it is not in man who walks to direct his steps.
Correct me, O LORD, but in justice;
not in your anger, lest you bring me to nothing.

Pour out your wrath on the nations that know you not,
and on the peoples that call not on your name,
for they have devoured Jacob;
they have devoured him and consumed him,
and have laid waste his habitation.

Jeremiah sees it as justice that he should be corrected in a way that gave him life, rather than destroyed him. He expects God”’s anger and wrath to be reserved for those outside the covenant (“the nations that know you not” and “the peoples that call not on your name.”)

For those in the covenant, sin is understood to be part of life and God is a wonderful covenant partner precisely because he forgives. Thus Psalm 130:

Out of the depths I cry to you, O Lord!
O LORD, hear my voice!
Let your ears be attentive
to the voice of my pleas for mercy!

If you, O LORD, should mark iniquities,
O LORD, who could stand?
But with you there is forgiveness,
that you may be feared.

I wait for the Lord, my soul waits,
and in his word I hope;
my soul waits for the LORD
more than watchmen for the morning,
more than watchmen for the morning.

O Israel, hope in the LORD!
For with the LORD there is steadfast love,
and with him is plentiful redemption.
And he will redeem Israel
from all his iniquities.

So what is it that marks one as a faithful covenant member who can depend on this great, forgiving God. The Apostle Paul said it in it most simple form to a prison guard: “Believe on the Lord Jesus Christ and you will be saved.”

As the Westminster Larger Catechism puts it:

The grace of God is manifested in the second covenant, in that he freely provideth and offereth to sinners a mediator, and life and salvation by him; and requiring faith as the condition to interest them in him, promiseth and giveth his Holy Spirit to all his elect, to work in them that faith, with all other saving graces; and to enable them unto all holy obedience, as the evidence of the truth of their faith and thankfulness to God, and as the way which he hath appointed them to salvation.

And consistent with this definition of covenant faithfulness (which itself is God’s gift to those fore-ordained to eternal life):

Q. 152. What doth every sin deserve at the hands of God?
A. Every sin, even the least, being against the sovereignty, goodness, and holiness of God, and against his righteous law, deserveth his wrath and curse, both in this life, and that which is to come; and cannot be expiated but by the blood of Christ.

Q. 153. What doth God require of us, that we may escape his wrath and curse due to us by reason of the transgression of the law?
A. That we may escape the wrath and curse of God due to us by reason of the transgression of the law, he requireth of us repentance toward God, and faith toward our Lord Jesus Christ, and the diligent use of the outward means whereby Christ communicates to us the benefits of his mediation.

Q. 154. What are the outward means whereby Christ communicates to us the benefits of his mediation?
A. The outward and ordinary means whereby Christ communicates to his church the benefits of his mediation, are all his ordinances; especially the word, sacraments, and prayer; all which are made effectual to the elect for their salvation.

Sinners sin, even believing sinners. But faith in Jesus Christ is what God requires of his covenant people. If they believe, they are being faithful to the covenant’s terms.

After all, when we read Peter’s response, does it make any sense to claim it is either a believing response or a faithful response because it can’t be both?

After this many of his disciples turned back and no longer walked with him. So Jesus said to the Twelve, “Do you want to go away as well?” Simon Peter answered him, “Lord, to whom shall we go? You have the words of eternal life, and we have believed, and have come to know, that you are the Holy One of God.”