The phrase is almost always followed by a declaration of God's sovereignty.
Then you will know that I am the Sovereign Lord. (Ezekiel 13:9)
Then you will know that I am the Lord your God. (Exodus 16:12)
Then you will know that I am in Israel, that I am the Lord your God, and that there is no other.
The phrase is almost always preceeded by a manifestation of God's presence, His power, His blessing or His judgement, particulary noted in Ezekiel's writing.
I will not look on you with pity; I will not spare you. I will surely repay you for your conduct and for the detestable practices among you. ‘Then you will know that I am the Lord.’ (Ezekiel 7:4)
The inhabited towns will be laid waste and the land will be desolate. Then you will know that I am the Lord. (Ezekiel 12:20)
I will put my Spirit in you and you will live, and I will settle you in your own land. Then you will know that I the Lord have spoken, and I have done it, declares the Lord.
In Exodus 6:7, the first time we see this phrase being used in the Bible, God says...I will take you as my own people, and I will be your God. Then you will know that I am the Lord your God, who brought you out from under the yoke of the Egyptians.
In Joshua, God says to the people...When you see the ark of the covenant of the Lord your God, and the Levitical priests carrying it, you are to move out from your positions and follow it. Then you will know which way to go, since you have never been this way before. (Joshua 3:3-4)
Isaiah writes...Then you will know that I am the Lord; those who hope in me will not be disappointed. (Isaiah 49:23) This has been my experience through all the ups and down on this journey of faith; though there may be some challenges, even heartaches along the way and there will be times when the way forward seems unclear, God is yet faithful and in putting my hope in Him, I am not disappointed.
Jesus said...When you have lifted up the Son of Man, then you will know that I am he. (John 8:28) From the suffering and shame of the cross, He is revealed as Savior and Lord, so that we can know the Father through Him. He also tells us in John 8:32...Then you will know the truth, and the truth will set you free. Aren't you glad that He has made truth known to us and that through that truth we are free indeed!
One of the great purposes of the written Word, the Holy Bible, is to reveal God to us so that we know that He is the Sovereign Ruler of All. May the Word become more precious to you in this season of life, so that you will know there is a God and He loves you; that you are in a covenant relationship with Him and His desire is to break into your live and lead you in ways that are consistent with His very best for you; that He will protect and provide for you and when your time on this earth comes to an end, He will lead you home. The you will know for all of eternity He is the Lord your God!