Short answers, pulled from the story.
The Narva Isthmus served as a natural choke point stretching 45 kilometres between Lake Peipus and the Gulf of Finland. This narrow strip forced armies into specific channels along the east-west axis where only the Narva-Tallinn highway could sustain large-scale troop movements.
Stalin issued a direct order on the 17th of February 1944 demanding the capture of Narva for military and political reasons. He later ordered his commanders to break through the defense line at Pärnu on the 22nd of February.
By summer 1944, seven infantry divisions and the Feldherrnhalle division left the front leaving only 22,250 troops at the location for the final phase of fighting. The III SS Panzer Corps deployed to Ivangorod Bridgehead while other corps held sectors against Krivasoo and Lake Peipus.
The Soviet vanguard attacked the Tannenberg Line on the 26th of July capturing part of Orphanage Hill before losing it back to German hands. Of the 136,830 Soviets initiating the offensive on the 25th of July, only a few thousand remained fit for combat by the 1st of August.
The underground National Committee of the Republic of Estonia convened on the 14th of February 1944. Acting head of state Jüri Uluots gave a radio speech on the 7th of February reasoning that armed Estonians could become useful against both occupiers.