AscendAscend on an instant or sorcery spell represents a spell ability. It means “If you control ten or more permanents and you don’t have the city’s blessing, you get the city’s blessing for the rest of the game.”
Ascend on a permanent represents a static ability. It means “Any time you control ten or more permanents and you don’t have the city’s blessing, you get the city’s blessing for the rest of the game.”
The city’s blessing is a designation that has no rules meaning other than to act as a marker that other rules and effects can identify. Any number of players may have the city’s blessing at the same time.
After a player gets the city’s blessing, continuous effects are reapplied before the game checks to see if the game state or preceding events have matched any trigger conditions. (CR 702.131) (If you control ten or more permanents, you get the city's blessing for the rest of the game.)
This creature has
double strikeDouble strike is a static ability that modifies the rules for the combat damage step. (See rule 510, “Combat Damage Step.”)
If at least one attacking or blocking creature has first strike (see rule 702.7) or double strike as the combat damage step begins, the only creatures that assign combat damage in that step are those with first strike or double strike. After that step, instead of proceeding to the end of combat step, the phase gets a second combat damage step. The only creatures that assign combat damage in that step are the remaining attackers and blockers that had neither first strike nor double strike as the first combat damage step began, as well as the remaining attackers and blockers that currently have double strike. After that step, the phase proceeds to the end of combat step.
Removing double strike from a creature during the first combat damage step will stop it from assigning combat damage in the second combat damage step.
Giving double strike to a creature with first strike after it has already dealt combat damage in the first combat damage step will allow the creature to assign combat damage in the second combat damage step.
Multiple instances of double strike on the same creature are redundant. (CR 702.4) as long as you have the city's blessing.