A monergist response to your verses would, I think, be along the lines of:
"Be perfect". We can have fellowship through Jesus taking our sins. In Christ we have His perfection. Who will be in Christ? Those that the Father has given Him. John 17:2 - " He should give eternal life to as many as you have given Him." "have given Him" It's a done deal.
"commandments". When God gives a command He either does or does not give the grace for that command to be obeyed. If His will is that someone obeys that command He gives them the grace to obey. If His will is that they do not obey He does not give the grace for that command to be obeyed. Only in this way can He be preeminent in all things. see Colossians 1: 18 "that in all things He may have the preeminence".
Rev 3:20. We choose to open or to leave shut. But, why do we choose one thing or another? We choose on the basis of who we are. Who are we? That depends upon how we were made.
We choose on the basis of how we were made. Judgement is having to live with the consequences of how we were made. Goats and sheep don't make themselves. Goats and sheep are separated on the basis of what they are, i.e. how God made them.
"Freedom". Gal 5:13. Freedom here is freedom from the Law, Old Testament Law, not freedom from some philosophic system of "free will".
[Our wills are not free of how and why God made them].
At one level monergism and synergism are about how people are saved but these spill over into wider issues about ultimate responsibility for evil. Synergism I suggest tries to protect God from the accusation that He is ultimately responsible for evil by saying something He created is autonomous from Him and this created evil. But synergism attacks God's uniqueness because by saying something other than God created evil it means that something other than God can create.
Monergists believe that at the start of every causal chain is one starting point, the Alpha of Rev 21:6. When God, who is light, created darkness [Isaiah 45:7] He had a holy motive for doing so. There is a single purpose behind everything in creation-"all things were created through Him and for Him", Col 1:16.