To God, marriage is a symbol of a unity that is intrinsic to his creation. From the Bible we find that people were designed with marriage in mind, so that it is part of our nature. But reaching further, it is also a relationship that may be abstracted and is echoed in the one we are called to develop with Jesus.
The basics of marriage are recorded right in the second chapter of the Bible, together with the creation of humans. It describes how a man and woman become joined into one entity,
Genesis 2:23: The man said, "This is now bone of my bones, and flesh of my flesh. She will be called Woman, because she was taken out of Man." 24 Therefore a man will leave his father and his mother, and will join with his wife, and they will be one flesh. WEB
This same statemet was later quoted by Jesus to show how divorce was wrong, and that it was to be a permanent bond between the two.
Matt 19:5: and said, `For this cause a man shall leave his father and mother, and shall join to his wife; and the two shall become one flesh?' 6 So that they are no more two, but one flesh. What therefore God has joined together, don't let man tear apart." WEB
This speaks of marriage as not so much as being a relationship between two people, but rather a joining of two people together. From this comes the classic statement of two people “being joined together in holy matrimony”. Such a joining necessitates a change in the people as they are no longer two individuals, but one individual.
This whole concept works against modern ideas of individualism, and instead has a model of a corporate individuality and identity. One seeks achievement and expression in the married unit rather than the individual person.
Joined to Christ
The view of marriage in the Bible doesn't stop with husband and wife. It is also used repeatedly in symbol to illustrate another relationship - that between people and Jesus. It draws on the attributes of marriage and applies them to how people relate to God. One example again uses that same principle outlined in Genesis,
1 Cor 6:15: Don't you know that your bodies are members of Christ? Shall I then take the members of Christ, and make them members of a prostitute? May it never be! 16 Or don't you know that he who is joined to a prostitute is one body? For, "The two," says he, "will become one flesh." 17 But he who is joined to the Lord is one spirit. WEB
Here it is applied to believers in Christ being joined to him in a way similar to marriage. Departure then, from following the way of Christ is like adultery. This same idea appears in 2 Corinthians,
2 Cor 11:2: For I am jealous over you with a godly jealousy. For I married you to one husband, that I might present you as a pure virgin to Christ. WEB
This unity is something that is important in a relationship with God. There is a requirement for both an integration and a dedication. Just as a marriage requires a new way of thinking, so does this symbolic marriage in Jesus. It means thinking in terms of being an inseparable part of a larger assembly.
In the book of Ephesians, there is a description of life in this entity,
Ephesians 5:25: Husbands, love your wives, even as Christ also loved the assembly, and gave himself up for it; 26 that he might sanctify it, having cleansed it by the washing of water with the word, 27 that he might present the assembly to himself gloriously, not having spot or wrinkle or any such thing; but that it should be holy and without blemish. 28 Even so ought husbands also to love their own wives as their own bodies. He who loves his own wife loves himself. 29 For no man ever hated his own flesh; but nourishes and cherishes it, even as the Lord also does the assembly; 30 because we are members of his body, of his flesh and bones. 31 "For this cause a man will leave his father and mother, and will be joined to his wife. The two will become one flesh." 32 This mystery is great, but I speak concerning Christ and of the assembly. WEB
Founded on Promise
This concept of marriage has its foundations in God's nation of ancient Israel. It was then that he outlined the promises that defined it. They were chosen as his special people, and he wanted them to be joined together with him. Speaking of Israel,
Isaiah 54:4: Don't be afraid; for you shall not be ashamed: neither be confounded; for you shall not be disappointed: for you shall forget the shame of your youth; and the reproach of your widowhood shall you remember no more. 5 For your Maker is your husband; Yahweh of Hosts is his name: and the Holy One of Israel is your Redeemer; the God of the whole earth shall he be called. WEB
Though they often left and were seduced by others, the mercy and patience of God is shown in how he always insisted that the promise would yet be fulfilled and that his chosen people would one day choose to be part of him.
Hosea 2:18: In that day I will make a covenant for them with the animals of the field, And with the birds of the sky, And with the creeping things of the ground. I will break the bow, the sword, and the battle out of the land, And will make them lie down safely.
19 I will betroth you to me forever. Yes, I will betroth you to me in righteousness, in justice, in loving kindness, and in compassion. WEB
Through Jesus, this offer is opened to everyone, and so God has proposed that we can be part of him. It isn't a toy relationship though, or something that can be done part-time. The basic principle of the relationship is the two becoming one as set down right from the start in Genesis.