To do this, I'll consider the relevant questions and answers from the Westminster Larger Catechism, interacting with each in turn to develop a complete sense of how we might prepare for communion.
Westminster Shorter Catechism question 97: What is required for the worthy receiving of the Lord's Supper?
A. It is required of them that would worthily partake of the Lord's Supper, that they examine themselves of their knowledge to discern the Lord's body, of their faith to feed upon him, of their repentance, love, and new obedience; lest, coming unworthily, they eat and drink judgment to themselves.
Note a few things of what the Catechism indicates a "worthy" receiving of the Supper consists of: the believer is to examine himself. Examining what? He "discerning" of the Lord's body, his faith, and the fruit of his faith. In other words, to receive the Lord's Supper in a "worthy" manner is to take it seriously, to acknowledge its significance and its weight, and to have a proper reverence and joy in what it represents.
The basis offered for the Catechism's answer-- the sole Scriptural evidence presented-- is 1 Corinthians 11:27-32. Here's that passage, plus the seven verses that precede it and the two after it (context is king!):
When you come together, it is not the Lord’s Supper you eat, for as you eat, each of you goes ahead without waiting for anybody else. One remains hungry, another gets drunk. Don’t you have homes to eat and drink in? Or do you despise the church of God and humiliate those who have nothing? What shall I say to you? Shall I praise you for this? Certainly not!
For I received from the Lord what I also passed on to you: The Lord Jesus, on the night he was betrayed, took bread, and when he had given thanks, he broke it and said, “This is my body, which is for you; do this in remembrance of me.” In the same way, after supper he took the cup, saying, “This cup is the new covenant in my blood; do this, whenever you drink it, in remembrance of me.” For whenever you eat this bread and drink this cup, you proclaim the Lord’s death until he comes.
Therefore, whoever eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty of sinning against the body and blood of the Lord. A man ought to examine himself before he eats of the bread and drinks of the cup. For anyone who eats and drinks without recognizing the body of the Lord eats and drinks judgment on himself. That is why many among you are weak and sick, and a number of you have fallen asleep. But if we judged ourselves, we would not come under judgment. When we are judged by the Lord, we are being disciplined so that we will not be condemned with the world.
So then, my brothers, when you come together to eat, wait for each other. If anyone is hungry, he should eat at home, so that when you meet together it may not result in judgment.
This is a full and weighty passage, and there is much in it that sometimes leads to controversy or disagreement. I won't give an exhaustive examination of the whole passage here, but I do want to touch on some highlights, particularly as they pertain to the Catechism question above.
First, note (as should be or become instinctive in Bible reading) that the relevant clause begins with "therefore"-- pointing us to what immediately precedes it. The fact that "a man ought to examine himself" (v. 28) and that he should recognize "the body of the Lord" (v. 29) is directly related to vv. 20-26-- especially vv. 20-22, where Paul describes the conduct of an unworthy participation in the Lord's Supper. "Recognizing the body of the Lord" has as its contrast v. 22's "do you despise the church of God". In other words, the "unworthy" manner is related to the manner of how the Lord's Supper is conducted, not the person participating.
Second, consider "worthiness" as it relates to this passage: could it possibly mean that some are deemed worthy to share in fellowship and communion with God Himself, by merit of their own work (even religious work, i.e., "proper" confessing of sin, etc.)? Or does it more likely mean that "worthiness" indicates a proper awareness of our desperate need for atonement apart from ourselves (and fulfilled in the work of Christ), which this sacrament "proclaims" (v. 26) to us and all around us? Thus, worthily discerning the body of Christ and participating in the Supper means that we long for it, as it represents and reminds us of Christ's great grace poured out for us.
Our Catechism isn't "finished" in helping us with the question about preparing our hearts for Communion, however. There is another helpful question and answer: Westminster Larger Catechism question 171: How are they that receive the sacrament of the Lord's Supper to prepare themselves before they come unto it?
A. They that receive the sacrament of the Lord's Supper are, before they come, to prepare themselves thereunto, by examining themselves of their being in Christ, of their sins and wants; of the truth and measure of their knowledge, faith, repentance; love to God and the brethren, charity to all men, forgiving those that have done them wrong; of their desires after Christ, and of their new obedience; and by renewing the exercise of these graces, by serious meditation, and fervent prayer.
Here again, we have a straightforward answer to the question: first and foremost, do you know yourself to be in Christ? To prepare oneself for the Sacrament is to be re-affirmed in faith.
The second part of that first clause, though, is where I think most will be hung up. "Of their sins and wants" might suggest that we should examine our sins and seek to "properly" name them in confession before God, else we should not participate in the Sacrament. Of course, this understanding is the opposite of what I proposed in my first discussion about this topic. Am I contradicted by the Catechism?
Grammatical construction helps us here: notice that, in the answer above, "examining themselves" is set up as the action relating to each of the different sets of things which should be examined. It's as if you could copy that phrase and paste it before each clause, like this:
...to prepare themselves thereunto, by examining themselves of their being in Christ, of their sins and wants; examining themselves of the truth and measure of their knowledge, faith, repentance; examining themselves [of the truth and measure of their] love to God and the brethren, charity to all men, forgiving those that have done them wrong; examining themselves of their desires after Christ, and of their new obedience; and by renewing...
You get the picture. So, how does the grammar help us? See that the Westminster Divines inserted a comma between "of their being in Christ" and "of their sins and wants"-- but a semicolon after it. In other words, they want us to see the association of the one with the other (by way of the comma) and the distinction of that clause with the rest. So when they urge an examination of our "sins and wants" it is in relation to, and in light of, our being in Christ. We are to prepare our hearts, first of all, by knowing the forgiveness and reconciliation for us in our redemption by and through Christ, and by recognizing our sins and wants as they are forgiven and swept away in Christ.
Likewise, the rest of the answer could be interpreted in a meritorious fashion as well: how much do I love God? How much can I point to the demonstration of my love for the brothers, and charity to all, and forgiveness of those who have wronged me? How much do I desire Christ, and demonstrate my obedience to Him? It's certainly possible to read the Catechism this way, and in so doing make the Sacrament one of two things (which it was never intended to be for us): either we convince ourselves that we do actually measure up to some degree of "worthiness" through all of those things, and it becomes a time of puffing up in arrogance, self-righteousness, and boastfulness; or we see clearly how much we fail to achieve any of those things even inadequately in ourselves, and it becomes a slavish reminder of how far we fall short all the time, in every way, and we loathe to even think of taking it.
Both of these results are clearly contrary to Scripture (as I demonstrated in brief in my previous piece). They are also contrary to the clear teachings throughout the rest of the Westminster Standards! Therefore, these other clauses should be understood rather to mean, in light of the first clause (that we are found in Christ, even in all of our sins and wants), we are to seek the fruit of our faith in Christ in these ways.
The final phrases in that answer lends further credibility to this interpretation: "and by renewing the exercise of these graces, by serious meditation, and fervent prayer." Why would we need to renew the exercises if we were already succeeding in them? What is the purpose of serious meditation and fervent prayer for the spiritually worthy and meritorious? But the presence of these concluding remarks expects shortcomings in that which precede them. Even in the assurance of being found in Christ!
I'll do one more part of this series, to wrap up by addressing the issue of assurance.