What does Mark 11:4 mean?

As God incarnate in human form, Jesus has chosen to limit use of His divine attributes, including omniscience. In short, as a fully-human man, Jesus does not actively know everything. For instance, He doesn't know when He will return (Mark 13:32). But He is guided by the Holy Spirit to know what He needs to obey the will of God the Father. Right now, He knows His entry will fulfill the prophecy found in Zechariah 9:9: that He will enter Jerusalem on the foal of a donkey. He also knows where the foal is and exactly what to say to the men who are guarding it (Mark 11:1–3).

This incident is not the same as what's today labeled "personal prophecy." Personal prophecy is the belief that God supernaturally gives people messages to be delivered to other specific people. Often, the "message" is that the recipient is supposed to give the prophet money. Since God's prophetic comments are typically not so specific, it is extremely unlikely –all but impossible—that God would directly tell one person to command another to donate money.

It's possible that God could give someone the discernment to know what will happen to another, but the belief in personal prophecy is more likely to be the cause of great spiritual abuse. It is not our job to tell others what to do.

Likewise, we are not obligated to obey the orders of another believer, even if they claim a message from God. Those who think they have received a prophecy on behalf of another should proceed with caution. At least, one can think of it as God's calling for them to pray for that person, that they will hear God's call personally. Actually taking such a claim to the person, especially when cast as a "prophecy," should be handled very carefully. For the one who is approached by someone who claims to have heard from God, they can listen respectfully and then pray for guidance.