Naqshbandi Mujaddidi way, A beautiful explanation
Wuqoof e qalbi means that we should at all times be attentive to Allah, never forget Him.
The example that our Hazrat gives is that if a man has to catch a flight in the evening, even if the whole day he is doing other unrelated chores, like picking his kids from school or buying groceries, he will never for even a minute forget that he has to catch a flight that evening. That doesn't mean he is actively thinking all the time that "I have a flight, I have a flight" but at the same time he will never forget.
Similarly the state of our heart should be to always remember Allah no matter what we are doing, but because our hearts have become so forgetful of Allah, to make the heart that way at first we have to consciously remind ourselves. For this we can try to think of the name of Allah, or be in a muraqabah-like state, but that is not wuqoof e qalbi itself, it is a way to achieve wuqoof e qalbi.
Imam e Rabbani, Mujaddid Alf Thani (rah) says that whenever we are doing something for the pleasure of Allah, or according to the shariah or sunnah, we are in a state of wuqoof e qalbi because we are mindful of Allah. And that is the goal, that our every move is in accordance to the Will of Allah (swt), we will only sin if for those moments we forget about Allah.
Like in Shaykh Mustafa's example, if someone is telling jokes with the intention to make others happy for the sake of Allah, and in telling those jokes he is conscious of staying within the bounds of shariah (so, for example, making sure that not a single word is a lie or hurtful or indecent), and if people are feeling happy with his jokes then he is feeling thankful to Allah, then even while telling those jokes he is in a state of wuqoof e qalbi.
When everything starts reminding u of Allah, and in making every move you think about how this move can be made to please Allah, this is wuqoof e qalbi.
But at first we need to force ourselves, because our hearts are not used to this. I remember once I told Hazrat ji that my head hurts because I am trying so hard to retain my concentration on Allah and he said that this is normal at first
But eventually it starts to come naturally, then even if you try to forget u can't. This means that even if for a moment u want to forget that Allah is watching and do a sin you won't be able to.
In the example of the man who has to catch a flight, by saying that he will never forget we mean that he will make sure that his chores don't take so long that they delay his departure for the airport, he will make sure that eventhough he has to do these chores he must pack his suitcases, he will make sure that in addition to these chores he must also convert his currency and do whatever else is needed for his travels. Same is the case with wuqoof e qalbi, that no matter what else we are doing in our day to day lives, we must make sure that the pleasure of Allah is not compromised, and that we are preparing for our meeting with Him.
Because just like if the man forgets about his flight he will be in danger of missing it and losing the chance to meet his family and friends waiting for him at his destination, if we forget about Allah we will be in danger of losing our chance to meet Allah in Jannah.
-by Ustadha Myra Kamal