Yeshua taught the people to love God and to love one another to enter the kingdom of heaven. A person should have TRUTH (follow laws) and LOVE (mercy) to be saved. Paul, on the other hand, says you are saved by Jesus' sacrifice on the cross and His resurrection. That we are saved by God's grace alone, and not by deeds.
Last November 1, I finally declared to the Lord that I believe in Yeshua's death and resurrection as the ultimate sacrifice that saved me. But I still asked Him and the Holy Spirit then to help me discern the truth between the two gospels. In today's "Bible study" (I put it in quotes as it was more of online research than Bible reading, hehe), the Lord answered my prayer for discernment :) It's now clear to me how the two gospels came about, and how it's NOT contradictory. Praise God!
As for the Christianity Today article (the first pink link above), the writer says Yeshua and Paul preached the same gospel because both tell the "story of Jesus who is Messiah and Lord, and who brings the kingdom and justifies sinners by faith." In other words, do NOT begin with the kingdom gospel (Yeshua's) or justification gospel (Paul's) in mind, instead, begin with Yeshua (as should be) and you will arrive to both the kingdom AND justification. Do read the article, quite good too :)
All in all, it has been a very productive afternoon for me, faith-wise. (Housework-wise, don't ask, hihi!) Anyway, if you are confused with the gospels or not sure if there's indeed a God (or supreme being / creator / etc), just go to a corner and pray (even for just this one time) for discernment. Ask God to show you, nay, REVEAL the truth to you. And He will. Maybe via websites like what happened to me; or maybe via the Bible directly, or via a friend's advice, etc. Just be ready to hear His loving voice.