Ex 20:3--"You shall have no other gods before Me."
The first commandment is the platform upon which God’s covenant with His people is built. Jesus said that we are to love God with all our being, quoting Deut 6:4-7--"Hear, O Israel! The LORD is our God, the LORD is one! You shall love the LORD your God with all your heart and with all your soul and with all your might."
"These words, which I am commanding you today, shall be on your heart. You shall teach them diligently to your sons and shall talk of them when you sit in your house and when you walk by the way and when you lie down and when you rise up."
Then Jesus added that the second commandment in importance is to love our neighbor as ourself, Lev 19:18--"You shall not take vengeance, nor bear any grudge against the sons of your people, but you shall love your neighbor as yourself; I am the LORD."
Apostle John taught us that we must love our brother if we claim to love God, 1 John 4:7-12--"Beloved, let us love one another, for love is from God; and everyone who loves is born of God and knows God. The one who does not love does not know God, for God is love."
"By this the love of God was manifested in us, that God has sent His only begotten Son into the world so that we might live through Him. In this is love, not that we loved God, but that He loved us and sent His Son to be the propitiation for our sins. Beloved, if God so loved us, we also ought to love one another. No one has seen God at any time; if we love one another, God abides in us, and His love is perfected in us."
There is one true God who revealed himself in creation and in human history. He appeared to Moses Ex 3:13-15--Then Moses said to God, "Behold, I am going to the sons of Israel, and I will say to them, "The God of your fathers has sent me to you.' Now they may say to me, "What is His name?' What shall I say to them?"
God said to Moses, "I AM WHO I AM"; and He said, "Thus you shall say to the sons of Israel, "I AM has sent me to you.'"
God, furthermore, said to Moses, "Thus you shall say to the sons of Israel, "The LORD (YHWH, Yahweh), the God of your fathers, the God of Abraham, the God of Isaac, and the God of Jacob, has sent me to you.' This is My name forever, and this is My memorial-name to all generations.’"
The descriptions of the Father are applied to Jesus, Isa 9:6--"For a child will be born to us, a son will be given to us; and the government will rest on His shoulders; and His name will be called Wonderful Counselor, Mighty God, Eternal Father, Prince of Peace."
Jesus is the Word of God who left heaven and became a man, as explained by Paul, Phil 2:5-11--"Have this attitude in yourselves which was also in Christ Jesus, who, although He existed in the form of God, did not regard equality with God a thing to be grasped, but emptied Himself, taking the form of a bond-servant, and being made in the likeness of men. Being found in appearance as a man, He humbled Himself by becoming obedient to the point of death, even death on a cross. For this reason also, God highly exalted Him, and bestowed on Him the name which is above every name, so that at the name of Jesus EVERY KNEE WILL BOW, of those who are in heaven and on earth and under the earth, and that every tongue will confess that Jesus Christ is Lord, to the glory of God the Father."
When we are loyal to Jesus, we fulfill the first commandment. Being loyal to Jesus requires putting him first, above everything else, except the Father, 1 Cor 15:27-28--For HE HAS PUT ALL THINGS IN SUBJECTION UNDER HIS FEET. But when He says, "All things are put in subjection," it is evident that He is excepted who put all things in subjection to Him. When all things are subjected to Him, then the Son Himself also will be subjected to the One who subjected all things to Him, so that God may be all in all.
All who are in Jesus Christ are one with him and with the Father, and have the Spirit of God within, the down payment on our eternal glory.