‘Above all things being fervent in your love among yourselves, for love covers a multitude of sins, using hospitality one to another without murmuring,'
Instead of indulging in ‘lasciviousness' (‘lustful living' - 1 Peter 4:3) they were to be fervent (‘at full gallop') in Christian love among themselves, because love counters much sin. And instead of indulging in wine-bibbing and revelry (1 Peter 4:3) they were to offer true hospitality towards one another in full unity and harmony, ‘without murmuring'. Such love would provide great strength in difficult times, and the hospitality might well have been necessary for those who were being persecuted, and even possibly having their houses burned and their goods spoiled. In their problems they were to turn to each other, and find help from each other. (Note that the hospitality is ‘one to another' as much as to those from outside).
‘Without murmuring' may indicate that they must not be grudging in their hospitality, or it may indicate that their hospitality must not be used as a means of backbiting, gossiping, talking about other people's sins behind their backs, making subversive plans or spreading rumours.
‘For love covers a multitude of sins' might be seen as having as a background Proverbs 10:12, ‘love covers all transgressions', which in the form in which Peter cites it may well have become a popular proverb. It is probably not a direct quote from the Old Testament because it is not in accordance with LXX, and it is the LXX which Peter usually quotes in this letter when citing the Old Testament, but if the words in MT had become an established proverb in Greek form well known in the churches then we can understand him citing it here, while at the same time having the Hebrew or Aramaic text of Proverbs in mind.
It may well be significant that in Proverbs the clause is preceded by, and in contrast with, ‘hate stirs up strifes'. This latter would tie in with Peter's ‘without murmuring (i.e. without causing strifes)'. Thus ‘love covers a multitude of sins --- using hospitality without murmuring' can be seen as conveying the sense of the whole verse in Proverbs, both positive and negative, but in reverse order from Proverbs (although not necessarily in reverse order from the proverb that had resulted from it). It is a reminder that love and hate are not actually simply revealed by what we profess, (what hypocrites we can be), but by how we truly behave, how we think about people and what we say behind people's backs. This connection with Proverbs would favour the meaning here that true love is the love that does not look censoriously upon the sins of others, but rather makes every reasonable excuse for them, and under no circumstances talks about them behind their backs (compare 1 Corinthians 13:4-13). Thus it ‘covers up a multitude of sins' in the right way. In other words love makes us ready to overlook people's many faults and thus be forgiving and merciful towards others. That does not mean that the sins do not matter. It means that we remember that we too are sinners.
But an added possible meaning of the words is that if we show true love towards our brothers and sisters by forgiving their sins in this way, then we can be sure that God will show His love for us in forgiving a multitude of our sins. This would tie in with Jesus' words in connection with the Lord's Prayer in Matthew 6:14-15. ‘For if you forgive men their trespasses, your heavenly Father will forgive you your trespasses.' Those words similarly provided an encouragement to show genuine love in this way. In other words the loving fellowship of Christians is one in which forgiveness is gladly given to others, covering up a multitude of sins, and is in turn joyously received from God, as He covers up for us an even greater multitude of our sins.
Comparison with James 5:20 may also, however, suggest the inclusion of a third thought and that is that by demonstrating love Christians will to some extent be compensating for a multitude of their own failures. All this explains why Jesus saw love as so important. It makes us better people, it makes us more considerate towards others, and it makes us the kind of people whom God can more easily forgive. >p> ‘Using hospitality one to another without murmuring.' This could well particularly have in mind the needs of Christians who were being dispossessed by persecution and required shelter (Acts 8:1; Hebrews 10:34), or, in a time when churches met in people's houses, the need for their homes to be always open to their brothers and sisters. Such hospitality was to be given unstintingly and without any grumbling. But hospitality was in fact a regular requirement for Christians (Matthew 25:35; Hebrews 13:2; Romans 12:13; 1 Timothy 3:2; Titus 1:8), and was a necessity for visitors because of problems related to inns, which were not of the highest standard and notorious as places of sin. And thus the exhortation must also be seen as having a more general application as well. But underneath it all is intended to lie the need for a willingness of heart to show practical love and concern for others.