These are
Olive trees give oil for the lamps on the two lampstands. Often in scripture the oil represents the Holy Spirit, so these two witnesses are filled with the Holy Spirit (Ephesians 5:18). Compare this description to Zechariah 4:1-14.
When witnessing (verse 7) or giving their testimony, they stand our as lights to the Jewish nation. Recall from the previous verse that under Old Testament methods, there are two or more witnesses required.
that stand before the LORD OF THE EARTH.
These two have a special place before the "Lord of the earth". Abram in Genesis 14:22 swore to "Lord God Most High, possessor of heaven and earth.".
After the destruction of the Jewish nation, God is referred to as the 'God of heaven'; for example Daniel 2:18, 37, 44. Here with this expression "Lord of the earth", God is again addressing Himself to the Jewish nation. They are witnessing in 'the Great City', verse 8.
Some scholars believe these two are not humans but angels in human form such as the ones at Christ's tomb, Luke 24:3-4, and at His ascension, Acts 1:10.