"Preaching" God's promises to yourself is an important practice that every Christian ought to develop.
My first exposure to the concept came by way of the book Spiritual Depression: Its Causes and Cure, a collection of sermons preached by Dr. Martyn Lloyd-Jones at Westminster Chapel in London some 40+ years ago.
In the first chapter Lloyd-Jones examines the words of the psalmist in Psalm 42 verses 5 and 11:
"Why art thou cast down, O my soul? and why art thou disquieted in me? hope thou in God: for I shall yet praise him for the help of his countenance...Why art thou cast down, O my soul? and why art thou disquieted within me? hope thou in God: for I shall yet praise him, who is the health of my countenance, and my God" (KJV, the translation used in the sermon).
"...we must learn to take ourselves in hand. This man was not content just to lie down and commiserate with himself. He does something about it, he takes himself in hand. But he does something which is more important still, that is he talks to himself" (p. 20).
"...I say that we must talk to ourselves instead of allowing 'ourselves' to talk to us! Do you realize what that means? I suggest that the main trouble in this whole matter of spiritual depression in a sense is this, that we allow our self to talk to us instead of talking to our self...Have you realized that most of your unhappiness in life is due to the fact that you are listening to yourself instead of talking to yourself?" (p.20).
Later Dr. Lloyd-Jones explains that,
"the main art in the matter of spiritual living is to know how to handle yourself. You have to take yourself in hand, you have to address yourself, preach to yourself, question yourself. You must say to your soul: 'Why art thou cast down' - what business have you to be disquieted?...and say to yourself: 'Hope thou in God' - instead of muttering in this depressed, unhappy way." (p. 21, emphasis added)
Lastly, Lloyd-Jones says,
"...you must go on to remind yourself of God. Who God is, and what God is and what God has done, and what God has pledged Himself to do. Then having done that, end on this great note: defy yourself, and defy other people, and defy the devil and the whole world, and say with this man: 'I shall yet praise Him for the help of His countenance, who is also the health of my countenance and my God''" (p. 21).
This is such wise and valuable instruction. I've benefited from it immensely over the years (even this past week!). So what are you waiting for? Start "preaching" to yourself.