The New Testament
The New Testament was written in Greek rather than Hebrew and therefore uses a different set of ways of referring to God.
The most commonly used word to refer to God in the New Testament is the Greek word 'Theos', which appears more than 1100 times in its pages. This is simply the ordinary word which refers to God; it has no special significance. The word is never applied to Jesus.
The word Theos is used to refer to God in this passage:
"The beginning of the gospel of Jesus Christ, the Son of God." (Mark 1:1)
This verse refers to two different people, Jesus Christ and God. The word 'Theos' is applied to God.
Another word which is sometimes applied to God is the Greek word 'Kyrios' which is usually translated as 'Lord'. The point about this word is that it is a word which does not need to refer to God.
Consider, for example:
"... as Sarah obeyed Abraham, calling him lord." (1 Peter 3:6)
Here the word is applied to Abraham, who is clearly not God. Nevertheless, Sarah, Abraham’s wife, showed him great respect by referring to him as Lord. This tells us that not everyone who is called Lord is God.
The difference between the word 'Lord' (Kyrios) and the word 'God' (Theos) is illustrated by the following passages:
"Grace to you and peace from God our Father and the Lord Jesus Christ," (Galatians 1:3)
Here it is clear that the word 'God '(Theos) is applied to the Father while the word 'Lord ' (Kyrios) is applied to Jesus Christ. This is because Jesus is very important and worthy of honour, but is not God.
"But thanks be to God, who gives us the victory through our Lord Jesus Christ." (1Corinthians 15:57) The passage again shows the difference between the word 'God' and the word 'Lord'. The word 'Lord' is applied to honour Jesus Christ, but the word 'God' is applied to the Father of Jesus, who is not Jesus.
"Therefore, as to the eating of food offered to idols, we know that 'an idol has no real existence', and that 'there is no God but one.' For although there may be so-called gods in heaven or on earth—as indeed there are many 'gods' and many 'lords' — yet for us there is one God, the Father, from whom are all things and for whom we exist, and one Lord, Jesus Christ, through whom are all things and through whom we exist." (1 Corinthians 8:4-6)
This passage contrasts the One God who has created the world with the 'gods' of the pagan Greeks. The pagan gods have no real existence, but there were statues of them in every Greek town. The real God is the Father of Jesus, and Jesus is called 'Lord' (Kyrios). The distinction is made very clearly in this passage.
While the word 'Lord' is usually used for Jesus, there are many places where the New Testament quotes passages from the Old Testament in which God would be referred to as JHWH. As the Jewish scholars of the time usually substituted the word 'Lord' for the name of God, the New Testament follows the practice of the time and uses the word 'Lord' in these passages where they are translated into Greek. Thus in passages like Acts 2:20, where the passage quotes from Joel 2:31 in the Old Testament. Joel 2:31 uses the word JHWH, but Acts translates this as 'Kyrios'. The English renders the word 'LORD' in the Old Testament and 'Lord' in the New Testament.
In some translations this can cause problems.