Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived; neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor homosexuals, nor thieves, nor the covetous, nor drunkards, nor revilers, nor swindlers will inherit the
kingdom of God.
The historical attitudes of Greek culture* as represented by Corinth toward homosexual behavior is the cultural context of the above scripture. In that context then, the two terms effeminate and homosexual would have carried specific meaning for Paul, and therefore, for the modern reader seeking to interpret the words. The first term refers to the male who receives the advances of a second (socially at the time, this would have been an adolescent not fully accepted as a citizen or a temple prostitute who was also not accepted as a full citizen). The second term refers to the initiator or dominating partner. In our modern social context of homosexuality these roles may or may not be fixed between two individuals. (Though female homosexuality was known in ancient times, there is little record to examine. From my observation within homosexual culture, a more "male" oriented partner usually occurs in same-sex couples of either gender.)
Homosexual marriage is not mentioned in the verse and some would say then is not prohibited. Is silence equal to condoning? I think an opposite inference makes more sense. The Greeks did not practice homosexual marriage.* The Jews certainly didn't. A Christian man who is deeply grounded in Jewish thought and practice speaking against behaviors to a culture that practices homosexuality but not homosexual marriage would have no reason to mention homosexual marriage separately in his rejection of the practice generally. It is more likely and certainly called for that he would speak of it separately, if he had viewed it as a blessed state before God. How else would he ensure no one construed his negative comments as applying to the that which God accepted?
Why listen to Paul? He had a very significant encounter with the Risen Jesus. Further the work of the Holy Spirit is real and relevant in his letters. There is a unity of thought throughout the New Testament, which taken with the Old Testament forms the basis for understanding the life, work and words of Jesus. To assert to be a follower of Jesus requires that Paul's writings be analyzed and applied to living in the present.
Finally, the practice of homosexual marriage does not and cannot reflect God's intentions in the establishment of marriage among humans. The big picture metaphor of the scriptures, the large message supported by all the stories and direct instruction, is a "marriage" for eternity between God and His beloved, the church. In creation, God had an original intent: God and humanity in an exchange of love. This relationship was broken but has been restored. In scripture, this restoration is a marriage metaphor of Jesus as the bridegroom and those pulled from the mire of human morality (or lack thereof) as a redeemed group called the bride.
Marriage is a sacred union of a man and a woman because these two opposite-gendered beings embody the fullness of God's eternal plan and are a picture of the eternal state of humanity with God. Two people of the same gender who are role-playing emotional states but are not able to actually join their physical bodies to create new life do not reflect the spiritual state with God humans need to understand.
The biology of a union between male and female is deeply significant. The various acts of sexual intimacy between two people of the same gender will never bring forth life. Two people of the same gender may commit to one another, may "marry" legally in some few states, may even adopt children and label all of this a function of their love for one another. However, none of these acts nor all together allow the two physical bodies to produce offspring. Science cannot intervene and cause two sperm or two eggs to produce a human embryo in vitro.
A living, holy, and infinite God has created humanity with the ability to procreate. This power may be misused and described incorrectly but nothing alters it. Beyond His creation, He has revealed Himself in human form to speak into our situation. Responding to Him makes it incumbent upon us to learn His definitions and live accordingly. Those blinded to Him will label all their activities acceptable as a function of the rebellion of the heart, but those who are in Him can never accept worldly substitutes for His divine wisdom and precept.