The following material comes from Michael G. Brown and Zach Keele, Sacred Bond: Covenant Theology Explored and Jerry Bridges, The Discipline of Grace: God's Role and Our Role in the Pursuit of Holiness.

Michael Brown and Zach Keele write:

The covenant of grace tells us that we are not under a covenant of works and therefore do not relate to God on the basis of our own law-keeping (Sacred Bond, 69). With its emphasis on the person and work of Christ, the covenant of grace tells us that we are not under a covenant of works. In the covenant of grace, God promises to accept us as righteous by virtue of the righteousness of His Son, the Second Adam. In other words, God’s covenant of grace draws attention to the doctrine of justification by faith alone. Whereas the covenant of works (law; Gen. 2:15-17) says, “Do this and you will live,” the covenant of grace (gospel; Gen. 3:15) says, “Christ did it for you. Live! Therefore, do this.” This distinction between the covenant of works (law) and the covenant of grace (gospel) allows us to go through life on the solid foundation that God receives us because of Christ.

For example, consider Q. 60 in the Heidelberg Catechism:

Q. 60. How are you righteous before God?

A. Only by true faith in Jesus Christ;1 that is, although my conscience accuses me that I have grievously sinned against all the commandments of God, have never kept any of them,2 and that I am still inclined always to all evil,3 yet God, without any merit of my own,4 out of mere grace,5 imputes to me the perfect satisfaction, righteousness and holiness of Christ,6 as if I had never had nor committed any sin, and as if I had myself accomplished all the obedience which Christ has fulfilled for me,7 if only I accept this gift with a believing heart.8

1 Rom 3:21-28; Gal 2:16; Eph 2:8-9; Php 3:8-11; 2 Rom 3:9-10; 3 Rom 7:23; 4 Deut 9:6; Ezek 36:22; Tit 3:4-5; 5 Rom 3:24; Eph 2:8; 6 Rom 4:3-5; 2 Cor 5:17-19; 1 Jn 2:1-2; 7 Rom 4:24-25; 2 Cor 5:21; 8 Jn 3:18; Acts 16:30-31; Rom 3:22

There is no greater contributing factor to our joy and comfort as Christians than the reality that God accepts us in spite of the fact that we still struggle with sin and disobedience. Knowing that God loves us on account of Christ protects us from the rollercoaster of our own conscience and emotions.

Jerry Bridges, A Good day/Bad Day Scenario

Consider two radically different days in your own life. The first one is a good day spiritually for you. You get up promptly when your alarm goes off and have a refreshing and profitable quiet time as you read your Bible and pray. Your plans for the day generally fall into place, and you somehow sense the presence of God with you. To top it off, you unexpectedly have an opportunity to share the gospel with someone who is truly searching. As you talk with the person, you silently pray for the Holy Spirit to help you and to also work in your friend’s heart.

The second day is just the opposite. You don’t arise at the first ring of your alarm. Instead, you shut it off and go back to sleep. When you finally awaken, it’s too late to have a quiet time. You hurriedly gulp down some breakfast and rush off to the day’s activities. You feel guilty about over-sleeping and missing your quiet time, and things just generally go wrong all day. You become more and more irritable as the day wears on, and you certainly don’t sense God’s presence in your life. That evening, however, you quite unexpectedly have an opportunity to share the gospel with someone who is really interested in receiving Christ as Savior. Would you enter those two witnessing opportunities with a different degree of confidence? Would you be less confident on the bad day than on the good day? Would you find it difficult to believe that God would bless you and use you in the midst of a rather bad spiritual day?

If you answered yes to those questions, you have lots of company among believers. I’ve described these two scenarios to a number of audiences and asked, “Would you respond differently?” Invariably, about 80 percent indicate that they would. They would be less confident of God’s blessing while sharing Christ at the end of a bad day than they would after a good one. Is such thinking justified? Does God work that way? The answer to both questions is no, because God’s blessing does not depend on our performance.

Why then do we think this way? It is because we do believe that God’s blessing on our lives is somehow conditioned upon our spiritual performance. If we’ve performed well and had a ‘good’ day, we assume we are in a position for God to bless us. Oh, we know God’s blessings come to us through Christ, but we also have this vague but very real notion that they are also conditioned on our behavior.

A friend of mine used to think, If I do certain things, then I can get God to come through for me. Such thinking is even stronger when we’ve had a ‘bad’ day. There is virtually no doubt in our minds that we have forfeited God’s favor for some period of time, most likely until the next day. I’ve asked people why they think God would probably not use them to share the gospel with someone on a ‘bad’ day. A typical reply is, ‘I wouldn’t be worthy,’ or ‘I would be good enough.’ Such a reply reveals an all-too-common misconception of the Christian life: the thinking that, although we are saved by grace, we earn or forfeit God’s blessings in our daily lives by our performance. . .

Here is an important spiritual principle that sums up what I’ve said thus far:

Your worst days are never so bad that you are beyond the reach of God’s grace. And your best days are never so good that you are beyond the need of God’s grace.

Every day our Christian experience should be day of relating to God on the basis of His grace alone. We are not only saved by grace, but we also live by grace every day. This grace comes through Christ, ‘through whom we have gained access by faith into this grace in which we now stand (Rom. 5:2).

A significant part of the Mosaic Law was the promise of blessings for obedience and curses for disobedience (see Deuteronomy 28, especially verses 1-2, and 15). Some Christians live as is that principle applies to them today. But Paul said that ‘the law (i.e., Mosaic covenant) was put in charge to lead us to Christ that we might be justified by faith’ (Galatians 3:24). Christ has already borne the curses for our disobedience (Gal. 3:13) and earned for us the blessings of obedience (Gal. 4:4). As a result we are now to look to Christ alone—not Christ plus our performance—for God’s blessings in our lives.

We are saved by grace and we are to live by grace alone. When we pray to God for His blessing, He does not examine our performance to see if we are worthy. Rather, He looks to see if we are trusting in the merit of His Son as our only hope for securing His blessing. To repeat: We are saved by grace, and we are to live by grace, and we are to live by grace every day of our Christian lives. If it is true that our relationship with God is based on His grace instead of our performance, when then are we so prone to fall into the good-day-bad-day type of thinking? It is because we have relegated the gospel to the unbeliever (The Discipline of Grace: God’s Role and Our Role in the Pursuit of Holiness, 13-15, 18-19).