At (one's) command formal
If a person "is at one's command", he/she is willing to obey or serve someone.
It was such a honor for me to be at your command. You're a great captain.
If you ever need anything, I will be at your command.
If someone has a particular skill or ability "at his/her command", he/she is capable of using it competently and effectively.
He protected himself in the war with all the weapons at his command.
The word "command" has a meaning of "order or direct with authority", it dates from c.1300
The inexplicable or concealed place or state indicates the afterlife.
I'm very sorry for your dad. He's beyond the veil.