Can man be saved and fall back into sin through temptation? Absolutly, David did. Can man be brought back into fellowship with God after these sins? David and many others did this as well. Realistically, every sinner does this on a daily basis.
When we look at what God thinks of sin, we must immediately realize that breaking laws intentionally is just as severe to God as murdering someone. You earn the same wage regardless how hard you work at sin (Rom 6:23). Where some try to reason that contemplating adultry, although a sin is not as severe as the actual act (Matt 5:28). If any one sin results in separating us from God’s presence, all sins in God’s eyes are the same, they all disqualify us from His presence in Heaven. There are no varying jail terms, no negotiable deals with the prosecutor, only one punishment for a sinner. It may not seem fair to you, but God wants His kingdom pure. Quite frankly, we’d engineer a work to get in there if it were any different. This way, the only way is through the blood of the Son of God, Jesus Christ. That is the way God wants it (1 John 5:9-13).
How do we tell though? Is it up to us to tell? Are we supposed to diagnose the heart of man? Are we supposed to be able to determine whether or not someone is saved? The short answer is “yes” and the long answer takes much more room than is here. However, we can point to a few pieces of scripture that tell us how to see this and the first one is through Christ as a man, not using His power as God to see man’s heart. That tells us through His humanity alone He could tell, and we should too.
John 8:40-44 and 1 John 3:15 enlighten us greately in this. In John 8:40 the temple leaders and other antagonists are seeking to kill Jesus, a fellow Jew for telling the truth. This truth is something they do not want to hear. To quiet Him they attempt to assassinate his character (kill Him publicly) and they have sought to grab Him to kill him bodily. They hate the truth, they hate even brothers who bring the truth, since God is truth (1 Kings 17:24), they hate God by association with truth. And, they hate a brother (1 John 3:15) so they hate God. These actions tell who they belong too, the one person who hates both God and man equally and seeks to destroy both, Satan.
We can also look at a simple passage, Galatians 5:17-25 which details the fruits of the spirit. It also contains something else, a testimony of flesh dominant life. Some on this list are hatred, variance, emulations, wrath, strife, seditions, heresies, envyings and murders. All of these attitudes are exhibited by those in the temple in John 8:2-59. They hate Jesus because people follow Him (hatred, envyings), they lie to deceive and create dissention (variance, emulations, wrath, strife, seditions, heresies) and they seek to kill either His character or His person (murder).
Ladies and gentlemen, what do you DO? Not to gain salvation, but what is the evidence of your salvation? What do you DO AFTER your salvation? What evidence can one mount to testify of your conversion to Christ? Do you find yourself loving, joyful, peaceful, longsuffering, gentle, good, faithful, meek and tempered? Are these growing and the others fading? That’s the test. Go with God, grow with God.