Shelia: Read Gal 3 but in particular verse 24, which says, "Wherefore, the law was our schoolmaster to bring us unto Christ, that we might be justified by faith." When you initially come to Christ, you learn the basics, as we did in school, as we did with the OT. When Jesus spoke in Matt 5:17-20, He had not yet gone to the Cross! Did you not hear him say in verse 17 that He "..did not come to destroy the law, or the prophets; I am not come to destroy, but to fulfill?" He fulfilled the law when He went to the Cross and shed His Blood for the remission of our sins! Verse 18 says "...till all be fulfilled..." Did He not fulfill the law by the shedding of His Blood?
Now, you must look at the laws under the New Covenant. Go to Jeremiah 31:33 (OT); Hebrew 8:10 and 10:16 which says, "This is the covenant that I will make with them AFTER THOSE DAYS (after He went to the Cross under the New Covenant: Grace and Truth), saith the Lord, I will put MY LAWS into their hearts, and in their minds will I write them." In John 14:26 Jesus said, "But the Comforter, who is THE HOLY SPIRIT, whom the Father will send in MY NAME, he shall TEACH YOU ALL THINGS, AND BRING ALL THINGS TO YOUR REMEMBRANCE, WHATEVER I HAVE SAID UNTO YOU." And He did in Acts Chapters 1 and 2 when the FIRST CHURCH was established!
Shelia, the OT is Jesus concealed and the NT is Jesus revealed! One cannot disregard the OT when the prophets were speaking of His coming; when It is "our schoolmaster!" However, in order to understand the Scripture one needs to pray and ask God for the Holy Spirit which will "...teach you all things..." Recall when Jesus was fulfilling the law while on earth, He fulfilled laws and under the NEW COVENANT He said, "I will put MY LAWS into their hearts, and in their minds will I write them." Revelation of Scripture is now being given individuals that has never been revealed before! Such as baptism! When the FIRST CHURCH was established, the apostles ONLY baptized in the name of the Lord Jesus and I am finding many Christians that have received the same revelation as well! The Holy Spirit is AWESOME! It does "lead and guide us into ALL truth." WE SERVE AN AWESOME GOD!
I pray that the "Holy Spirit" lead and guide you into ALL Truth! Stay Blessed!