We can be obedient in our Christian walk. Scripture says that if we walk in the Spirit, we will not fulfill the lusts of the flesh. (Galatians 5:15) Our faithful walk, however, is interrupted daily by the world, the flesh and the devil, the cares of this world and the deceitfulness of riches.
Despite these challenges, we can reposition ourselves and get back into the Spirit. We can insist on obeying God and going to His Word for fortification. (Psalm 119:105) I don't mean being persistent in trying to obey the Ten Commandments.
To say that No we can never be obedient, if it was humanly possible then Jesus wouldn't have had to come, refers to fulfillment of the Ten Commandments. It is true that we can never fulfill the requirements in the Ten Commandments, no matter how good we strive to be. God never expected us to.
The Ten Commandments was given to show up sin, to illuminate it, to show man the truth about the works of the devil. (Romans 7:15-20) We don't have to fear the Ten Commandments, an edict that we can never fulfill. Jesus fulfilled them all on our behalf. That's why He gave His Pure Blood and Unblemished Body on The Cross.
When it comes to daily obedience to the prompting of the Holy Spirit, we can then choose to obey or not. Obedience is always available to us. We can obey every single time that we perceive that God is speaking to us, however He may do it.