It is essential to say grand old truths again and again. There is ample evidence in the Bible that they are quickly forgotten.
Remember, there are different kinds of forgetting.
One is that great truths are gone out of the mind never to return. The other is that they are gone out of the mind for a season (a day, a year) while we languish in discouragement and sin.
Don’t follow Israel here:
“And the people of Israel did not remember the LORD their God, who had delivered them from the hand of all their enemies on every side.” (Judges 8:34)
Rather, submit to Peter:
“I intend always to remind you of these qualities, though you know them and are established in the truth that you have. I think it right, as long as I am in this body, to stir you up by way of reminder.... This is now the second letter that I am writing to you, beloved. In both of them I am stirring up your sincere mind by way of reminder.” (2 Peter 1:12-13; 3:1)