Can you tell me what the phrase "house of prayer" means from Matthew 21:13? Is this word used as a synecdoche or is it meant to mean literal "prayer?" If prayer was not the only thing they did at the temple, could this word have been used to mean a house of 'worship?'
Jesus is quoting two passages:
"Even those I will bring to My holy mountain And make them joyful in My house of prayer. Their burnt offerings and their sacrifices will be acceptable on My altar; For My house will be called a house of prayer for all the peoples" (Isaiah 56:7).
""Has this house, which is called by My name, become a den of robbers in your sight? Behold, I, even I, have seen it," declares the LORD" (Jeremiah 7:11).
A synecdoche is when a part is used to represent the whole or when the whole is used to represent a part. Even in the quote from Isaiah we can see that prayer is not the only thing that took place at the Temple, sacrifices happened as well; though, of course, prayers typically accompanied the sacrifices, as can be seen in Daniel: "While I was still speaking in prayer, then the man Gabriel, whom I had seen in the vision previously, came to me in my extreme weariness about the time of the evening offering" (Daniel 9:21). There was a morning and evening offering and this was the common time for the Israelites to pray. "May my prayer be counted as incense before You; The lifting up of my hands as the evening offering" (Psalms 141:2).
The Temple was intended as a place where worshipers could come and pray to God. "Now therefore, O God of Israel, let Your word, I pray, be confirmed which You have spoken to Your servant, my father David. But will God indeed dwell on the earth? Behold, heaven and the highest heaven cannot contain You, how much less this house which I have built! Yet have regard to the prayer of Your servant and to his supplication, O LORD my God, to listen to the cry and to the prayer which Your servant prays before You today; at Your eyes may be open toward this house night and day, toward the place of which You have said, 'My name shall be there,' to listen to the prayer which Your servant shall pray toward this place" (I Kings 8:26-29). Therefore, to refer to the Temple as a house of prayer is to acknowledge one of the purposes for which the Temple existed.