It should be obvious from the context that this promise does not refer to whatever two or three disciples agree to ask God for in prayer. The Bible contains many promises concerning prayer (cf. Matthew 7:7-8; Matthew 21:22; John 14:13-14; John 15:7-8; John 15:16; 1 John 5:14-15; et al.), but this is not one of them. [source][source][source]
In the context "anything" refers to any judicial decision involving an erring disciple that the other disciples may make corporately. God has always stood behind His judicial representatives on earth when they carry out His will (cf. Psalm 82:1). This is a wonderful promise. God will back up with His power and authority any decision involving the corporate discipline of an erring brother or sister that His disciples may make after determining His will. [1][source]
Here again ( Matthew 18:20) Jesus takes God"s place as "God with us" ( Matthew 1:23; Matthew 2:6; Matthew 3:3; Matthew 11:4-8; cf. Matthew 28:20). This statement implies a future time when Jesus would not be physically present with His disciples, the inter-advent age, specifically the period following His ascension and preceding His return. Jesus anticipated His ascension. [source][source][source]
One writer argued that Matthew 18:18-20 are the center of a structural and theological chiasm that embraces Matthew 17:22 to Matthew 20:19. [2] This thesis seems a bit stretched to me. [source][source][source]