No, Jesus' teachings in the Gospels clearly show no man can be "justified" in the sight of Father God because all have fallen short, and failed at the 10 commandments. This is why Jesus is "the way, the truth, and the life" whereby no man can get access to Father God, but through Him. In other words, Jesus did what no man could do: Walk sinless, and die for sinful people.
Moreover, the Old Testament prophets plainly declared that Jesus would come to save Jews as well as gentiles.
How are believers "justified" in the sight of God? By faith in Jesus' work of the cross to justify us. Moving forward from there, as a Christian walks out their faith according to the New Testament teachings, they grow in the knowledge of God and mature. When a Christian stumbles, they lean upon God's grace, and call upon Him to empower them to overcome sin in their lives (knowing they could never justify themselves, and appreciating Jesus' work of the cross).
That being said, you cannot be a Christian and practice certain things. For example, you can't be a Christian and cheat on your wife. God didn't send His only begotten Son to die for the sins of people so He could rubber-stamp their wicked ways. God will empower those, and give them a way of escape from such wicked practices, when the temptation comes to do such things.