Love is one of the basic emotions, described as an extreme affection for a person, an object, an idea, a country, a friend or a family member. Love is used to describe affection for many different things, but can sometimes be misinterpreted for Lust.
Many faiths, such as Christianity, Judaism, Buddhism, etc., believe love to be a positive trait, and the followers of these religions are asked to practice love for others as a general principle for a good life.
The Five Grecian Forms
The ancient Greeks identified four forms of positive love:
- Philos - the love of close friends or brothers. Aristotle identifies several types of philos  which can include utility as well as shared characteristics and values. The word is often attached to groups of people who share a love of a common pursuit.
- Storge - the love of family. This would include patriotism - the love of country or homeland. Storge was a word used by the Greeks to describe a strong love that protects and makes secure.
- Eros - carnal or sexual love. This would include romantic love but would also include lust. Eros is intended by God, as laid down in the Bible, to be enjoyed between a married man and woman. The Greek word epithumia spoke of desire that found its fulfillment in sexual love.
- Agape - love which seeks the highest good of others, not just friends, family or brothers, but including enemies. This is considered by all major world religions to be the highest kind of love, although Buddhism would regard it as compassion. Agape is most often used to speak of God's love and in the days of biblical times it described love in its most profound and pure form. Apostle Paul chose the word agape for his description of love in 1.Corinthians 13.
The fifth form of love is called Narcissism, or self-love. This word comes from the Greek myth of Narcissus, who fell in love with his own reflection. Although Freud considered that everybody has some degree of narcissism, and that this is present in us from birth, if taken to extremes narcissism can be considered a personality disorder. 
The bible mentions love, especially Agape, repeatedly.
For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life.
Know therefore that the LORD your God is God; he is the faithful God, keeping his covenant of love to a thousand generations of those who love him and keep his commands.
I love those who love me, and those who seek me find me.
Pauline DefinitionHenry Drummond referred to 1 Corinthians 13:4-7 when he wrote,
As you have seen a man of science take a beam of light and pass it through a crystal prism, as you have seen it come out on the other side of the prism broken up into its component colors—red, and blue, and yellow, and violet, and orange, and all the colors of the rainbow—so Paul passes this thing, Love, through the magnificent prism of his inspired intellect, and it comes out on the other side broken up into its elements.
The Pauline definition in 1 Corinthians 13:4-7:
4 Charity suffereth long, and is kind; charity envieth not; charity vaunteth not itself, is not puffed up, 5 Doth not behave itself unseemly, seeketh not her own, is not easily provoked, thinketh no evil; 6 Rejoiceth not in iniquity, but rejoiceth in the truth; 7 Beareth all things, believeth all things, hopeth all things, endureth all things. (KJV)
Love is patient and kind; love does not envy or boast; it is not arrogant or rude. It does not insist on its own way; it is not irritable or resentful; it does not rejoice at wrongdoing, but rejoices with the truth. Love bears all things, believes all things, hopes all things, endures all things. (ESV)
Love never gives up.
Love cares more for others than for self.
Love doesn’t want what it doesn’t have.
Love doesn’t strut,
Doesn’t have a swelled head,
Doesn’t force itself on others,
Isn’t always “me first,”
Doesn’t fly off the handle,
Doesn’t keep score of the sins of others,
Doesn’t revel when others grovel,
Takes pleasure in the flowering of truth,
Puts up with anything,
Trusts God always,
Always looks for the best,
Never looks back,
But keeps going to the end. (The Message)
Clementine Definition 
In the early Christian writer Clement's Epistle to the Corinthians, we read:
Love unites us to God. Love covers a multitude of sins. Love beareth all things, is long-suffering in all things.There is nothing base, nothing arrogant in love. Love admits of no schisms: love gives rise to no seditions: love does all things in harmony. (John Keith)
Charity unites us to God; charity covers the multitude of sins: charity endures all things, is long-suffering in all things. There is nothing base and sordid in charity; charity lifts not itself up above others; admits of no divisions; is not seditious; but does all things in peace and concord. (Wake)
Love unites us with God; love covers a multitude of sins; love endures everything, is long-suffering to the last; there is nothing vulgar, nothing conceited, in love; love creates no schism; love does not quarrel; love preserves perfect harmony. (Quasten and Plumpe)
Christian Commentators 
- Barnes & Murphy: There were contentions and strifes among [the Corinthians]; there were of course suspicions, and jealousies, and heart-burnings; there would be unkind judging, the imputation of improper motives, and selfishness; there were envy, and pride, and boasting, all of which were inconsistent with love; and Paul therefore evidently designed to correct these evils, and to produce a different state of things by showing them what would be produced by the exercise of love.
- Joseph Beet: Whereas gifts without love are worthless, love even without gifts retains its value undiminished. No stronger proof of the value of love can be given. ... It is a principle of action prompting us to use our powers and opportunities for the good of others, and to draw them to us that we may share, and thus remove, their sorrow, and that they may share our good. This principle appears, more or less perfect and intelligent, in all true human love. It is the mainspring of the entire activity of God. And so far as it rules our conduct are we like God.
- E.W. Bullinger: These two words are not used indiscriminately. Agapaô, never means to kiss; fileô, never means to acquiesce or cherish with reverence. Fileô denotes the sense or passion of love, but in agapaô is implied the cause of fileô. Agapaô is to make much of a thing, to admire for some good and sufficient reason, but fileô denotes the love which springs naturally from the thing loved, even where no just cause of love exists. Agapaô is never used of an improper love; fileô is. Hence, in the N.T. fileô is never used of man's love to God, but agapaô always.
- Stephen J. Cole: Paul enumerates 15 characteristics of love to show how love acts or what it looks like in everyday life. A New Testament definition of agape is “a caring, self-sacrificing commitment which shows itself in seeking the highest good of the one loved.”
- Lee Gatiss: This is the sort of love which, if universally practiced, would put an end to all the divisions in the Church.
- Matthew Henry: How good-natured and amiable is Christian charity! How excellent would Christianity appear to the world, if those who profess it were more under this Divine principle, and paid due regard to the command on which its blessed Author laid the chief stress! Let us ask whether this Divine love dwells in our hearts.
- W. Robertson Nicoll: The loftiest human faculties of man are seen to be frustrate without love; by its aid alone are they brought to their proper excellence and just use.
Atheism and its inability to explain love
- See also: Atheism and love
- Aristotle, Nicomachean Ethics, Book VIII
- Thomas Nelson. David Sper:What Is Real Love?. RBC Ministries.
- Matthew 5:44
- Freud, Sigmund, On Narcissism: An Introduction, 1914
- Bible Verses on Love - God’s Love For Us. AllAboutGOD.com.
- http://www.strangenotions.com/atheists-love/ How do atheists define love?
- https://atheistforum.wordpress.com/2014/07/09/what-is-love-how-materialist-atheism-fails-to-have-a-satisfactory-answer/ What is love? how materialist atheism fails to have a satisfactory answer, July 9, 2014