When David, King David, spoke of waiting on the Lord he was likely referring to the awkward space that patience requires before prayer is answered.
It is simply, and annoyingly, a time to wait.
And it is the domain of trust, which is something not easy for people who are active, and therefore not the modus operandi of most kings.
“I believe that I shall look on the goodness of the Lord in the land of the living! Wait for the Lord; be strong, and let your hearty take courage; wait for the Lord?” Ps 27:13-14. This is a man, a woman, who is literally waiting to see something they anticipate they will see. Waiting is equated with time and patience. Also, “Be still before the Lord and wait patiently for him.” Ps 37:7. Waiting is waiting. Patience is what waiting requires. Being ‘still’ is not about, not moving around, but about refusing to be agitated and anxious in the process of waiting. And waiting also assumes we are getting on with normal living, with its myriad demands and responsibilities.
But this doesn’t exhaust the meaning of waiting on the Lord. It can also refer to the learned practice of silent prayer, as in waiting on the presence and voice of the Holy Spirit. Those in a constant and nervous rush miss this means of hearing God communicate by his Spirit to them. It was likely this that Joshua learnt when he lingered in the tent of meeting after Moses had gone out. Exodus 33:11. “Thus the LORD used to speak to Moses face to face, as a man speaks to his friend. When Moses turned again into the camp, his assistant Joshua the son of Nun, a young man, would not depart from the tent.” Whatever transpired in the tent with the young Joshua we can be sure that this was part of the reason he was chosen by God and prospered in his vocation. He stayed. He lingered. He waited. He heard.
At very least he did what we can do, and that is to create the capacity and the space to hear from God. It is a discipline. It takes time, and it is not as though God speaks every time. But what is certain to happen is that we open a door to hear. We gain the skill of having our ears opened to be able to listen when God does speak. Whether or not we hear then and there or at some other time (which it often seems to be), we have made room for God, we have stilled the noise of the world we live in (and have to), so as to be able to hear the whisper of the Almighty. He rarely shouts. He mostly intimates, whispers, and/or gently impresses something on us.
Unless you wait you won’t hear - more to the point, you can’t hear. Not having a capacity for something is the same as not being able to do something.
Wait on the Lord. Be still. Take time. Be silent. Calm the noise. Hear the voice of your Lord and God.