“keep asking.” The verb for “ask” in this verse is in the active voice, present tense, and imperative mood. The present tense in this case is what is known as a broadband present, or continuous present (Cp. Wallace, Greek Grammar, pg. 519-25). This form indicates a continual action that takes place over a long time, rather than a one-time-event. We are not to just ask once for the things we seek from God, but to repeatedly ask, just as the widow kept asking the unjust judge (Luke 18:1-8). Wallace explains the present tense here in Matthew 7:7 this way: “The force of the present imperatives is ‘ask repeatedly, over and over again…seek repeatedly… knock continuously, over and over again” (Wallace, Exegetical Syntax, 521). The imperative mood is the mood of command or of exhortation. Jesus is not just making a statement that we should ask, as if he thinks it would just be a nice thing to do. He is making an impassioned plea, an earnest exhortation that believers ask for what they need.
One of the faults that Christians have is that they stop praying for things before they get an answer. Of course there are times when we learn that something we are praying for is not God’s will. In that case, we should stop praying for that thing. Also, there are times when we are praying that the circumstances change, such as if we are praying for a sick person to get healed but they die, which occasionally happens. In these cases, too, we should stop praying. But otherwise we need to be like the persistent widow in Luke 18 who keeps coming to the judge time after time. We need to pray and pray and pray. When Daniel wanted an answer from God about the revelation he received from God, he prayed for three weeks (Dan. 10:2) before he got an answer, and we do not know how much longer he would have prayed if an answer had not come to him when it did.
Some Christians teach that is disrespectful of God, or shows a lack of trust (“faith”), if we pray more than one time for something. Their theology is that if you pray one time with trust, that is enough, and then just wait for the prayer to be answered. That sounds good, but it is unbiblical. The Bible says if we want to get our prayers answered we are to keep praying for what we want, keep asking, and keep knocking. Cp. Luke 11:9, John 16:24, and commentary on 1 John 3:22.
“keep seeking, and you will find.” God said basically the same thing to the Judeans (Jer. 29:13).