Hebrews 2:1 (NKJV)
If you have a boat, there are things you need to do to take care of it. One thing that is necessary with a boat, when it is in the water, is to have it anchored or tied to a dock, or something else. If you do not use an anchor or tie up the boat, it will eventually just drift away. No one would intentionally let their boat get away from them, but unless the boat is secured in some way, sooner or later that boat will be gone. How far away the boat drifts depends on several factors, but without something to keep it in place, the boat will drift away.
It is good to hear God's Word and learn about who God is, what Jesus has done for us, who we are in Christ, and what God has planned and provided for us. But it is not enough just to hear about this one time, this is something we need to hear about, read about, think about, and talk about again and again. Making what we hear a part of our life is an important way to make sure that what we know and understand is more than just something nice that we have heard.
As Hebrews 2:1 tells us, we need to pay attention to what we have heard, so that those things do not slip away from us. If we hear the truth, but do not do anything with the truth that we hear, that truth can slip away from us. The problem for many Christians is not that they have not heard and do not know the truth, but the trouble is that the truth they have heard has slipped away from them. We need to not only learn God's Word, but we need to make it a part of our life so that it does not slip away from us.