1 Corinthians 14:21 in the King James Version reads: "In the law it is written, with men of other tongues and other lips will I speak unto this people; and yet for all that will they not hear me, saith the Lord."

In this verse, the apostle Paul is quoting from the Old Testament, specifically from the book of Isaiah. The context of this verse is Paul's instructions to the Corinthian church regarding the use of spiritual gifts, particularly the gift of speaking in tongues.

Paul is emphasizing the importance of prophecy over the gift of tongues, as prophecy is meant for edification, exhortation, and comfort within the church, while speaking in tongues without interpretation may not benefit the congregation as a whole. In doing so, Paul uses this quote from Isaiah to illustrate the idea that speaking in tongues, without interpretation, will not necessarily lead to understanding or conviction among the listeners.

The verse in Isaiah that Paul is quoting comes from Isaiah 28:11-12, which reads: "For with stammering lips and another tongue will he speak to this people. To whom he said, This is the rest wherewith ye may cause the weary to rest; and this is the refreshing: yet they would not hear."

The original context of the verse in Isaiah is a rebuke against the people of Judah for their unbelief and rejection of God's message. The prophet Isaiah had been sent by God to warn the people of impending judgment, yet they refused to listen. So, they were going to be judged by foreign invaders who would speak a language the people would not be able to understand. This foreign invasion was meant to be a punishment for their disobedience and rejection of God's word.

When Paul applies this verse to the Corinthian church, he is warning them about the danger of pursuing spiritual gifts for the wrong reasons and using them in a way that does not edify or benefit the body of believers. He is reminding them that the purpose of spiritual gifts is to build up the church and to bring glory to God, not to serve one's own ego or to create confusion and division within the community of believers.

The themes present in this verse include the importance of understanding and edification in the church, the proper use of spiritual gifts, and the consequences of rejecting God's message. It also highlights the idea of judgment and consequences for disobedience.

Symbolically, the use of tongues can represent the diversity of languages and cultures in the world, and the need for effective communication in sharing the gospel with all people. It can also symbolize the potential for division and confusion when not used in a way that is guided by love and proper understanding.

Overall, 1 Corinthians 14:21 serves as a reminder to the Corinthian church, and to us today, about the importance of using spiritual gifts in a way that glorifies God and builds up the body of believers. It also serves as a warning about the consequences of rejecting God's message and the need for humility and obedience in our pursuit of spiritual gifts.