Jesus meant two things by saying God will give the Holy Spirit to all who ask. First, he meant that God would give his presence to any who ask. Secondly, he meant that God would enlighted our minds for us to recognize the truth.
You may say that God always gives us himself to be with us. But sometimes his presence to us is like that of an old book that we never take off its shelf. But what Jesus is promising here is that God's presence with us would be like that of a great book we can never lay down,
Secondly, by telling us he would give us the Holy Spirit, Jesus was saying that the Spirit would be with us to lead us to all truths. He shakes up our minds to bring the right answer to the surface.