"For the preaching of the cross is to them that perish foolishness; but unto us which are saved it is the power of God." (1 Corinthians 1: 18)
We do not leave the Gospel and move onto other things in our lives.
The Gospel, the Good News of all that Jesus did for us at the Cross, is our meat and drink every day:
"Even so hath the Lord ordained that they which preach the gospel should live of the gospel." (1 Corinthians 9: 14)
Let us remember what the Good News is, in its fullest:
"Be it known unto you therefore, men and brethren, that through this man is preached unto you the forgiveness of sins: 39And by him all that believe are justified from all things, from which ye could not be justified by the law of Moses." (Acts 13: 38-39)
Paul wrote in greater detail to the Corinthians:
"20Now then we are ambassadors for Christ, as though God did beseech you by us: we pray you in Christ's stead, be ye reconciled to God. 21For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him. (2 Corinthians 5: 20-21)
To the Ephesians:
"But God, who is rich in mercy, for his great love wherewith he loved us, 5Even when we were dead in sins, hath quickened us together with Christ, (by grace ye are saved;) 6And hath raised us up together, and made us sit together in heavenly places in Christ Jesus: 7That in the ages to come he might shew the exceeding riches of his grace in his kindness toward us through Christ Jesus." (Ephesians 2: 4-7)
Also consider what Paul wrote to the Colossians:
"13And you, being dead in your sins and the uncircumcision of your flesh, hath he quickened together with him, having forgiven you all trespasses; 14Blotting out the handwriting of ordinances that was against us, which was contrary to us, and took it out of the way, nailing it to his cross; 15And having spoiled principalities and powers, he made a shew of them openly, triumphing over them in it." (Colossians 2: 13-15)
Now, we have indeed been saved, taken from death to life in Christ Jesus (1 John 3: 14), but we are called to grow in grace and knowledge of the Lord, too (2 Peter 3: 18)
So, we do not just understand the gift of righteous when we first believe, but we continue to receive:
"15But not as the offence, so also is the free gift. For if through the offence of one many be dead, much more the grace of God, and the gift by grace, which is by one man, Jesus Christ, hath abounded unto many. 16And not as it was by one that sinned, so is the gift: for the judgment was by one to condemnation, but the free gift is of many offences unto justification. 17For if by one man's offence death reigned by one; much more they which receive abundance of grace and of the gift of righteousness shall reign in life by one, Jesus Christ." (Romans 5: 15-17)
We keep receiving the gift of righteousness and the abundance of grace.
And we keep being transformed from glory to glory as we see more of Jesus! (2 Corinthians 3: 18)
The Gospel is not just a one-time account which we hear, then move onto other things. The Gospel, the Good News of our full justification in Christ Jesus, is a revelation which we keep hearing, believing, and receiving, and we then witness Jesus keep achieving His Good Work in us!