Hi Narkissos,
I do not want to be contentious but I fail to see the problem between the two scriptures you have posted? Here they are.
Romans 10:9 (New International Version)
9 That if you confess with your mouth, "Jesus is Lord," and believe in your heart that God raised him from the dead, you will be saved.
Matthew 7:21 (New International Version)
21 "Not everyone who says to me, 'Lord, Lord,' will enter the kingdom of heaven, but only he who does the will of my Father who is in heaven.
So what do you find in one that is contrary to the other? Here is the will of the Father explained.
John 6:40 (New International Version)
40 For my Father's will is that everyone who looks to the Son and believes in him shall have eternal life, and I will raise him up at the last day."
Once again, it is about belief in Jesus. Quite obviously, not everyone who says "Lord, Lord" will enter the Kingdom.
Consider Jehovah's Witnesses for example. Ask them and they will say "Jesus is Lord", no problem, it is in the NWT after all. However, do they believe that God raised Him from the dead as the scripture says? No, they do not. They say Jesus was raised as a "spirit creature". Now a spirit has no body (some would call it a ghost). Nowhere does the bible say Jesus was raised as a ghost or even a "spirit creature". Nowhere. They twist this verse to their own destruction
1 Peter 3:18 (New International Version)
18 For Christ died for sins once for all, the righteous for the unrighteous, to bring you to God. He was put to death in the body but made alive by the Spirit
How was Jesus raised from the dead? By the power of the Holy Spirit. Who is He? The Spirit of God (verse 9 below) who is also the Spirit Of Christ (verse 9 also)
Romans 8:9-11 (New International Version)
9 You, however, are controlled not by the sinful nature but by the Spirit, if the Spirit of God lives in you. And if anyone does not have the Spirit of Christ, he does not belong to Christ. 10 But if Christ is in you, your body is dead because of sin, yet your spirit is alive because of righteousness. 11 And if the Spirit of him who raised Jesus from the dead is living in you, he who raised Christ from the dead will also give life to your mortal bodies through his Spirit, who lives in you.
Jesus Himself said He was not a ghost or just spirit. See below, the disciples touched His physical body as the scripture says.
Luke 24:38-42 (New International Version)
38 He said to them, "Why are you troubled, and why do doubts rise in your minds? 39 Look at my hands and my feet. It is I myself! Touch me and see; a ghost does not have flesh and bones, as you see I have."
40 When he had said this, he showed them his hands and feet. 41 And while they still did not believe it because of joy and amazement, he asked them, "Do you have anything here to eat?" 42 They gave him a piece of broiled fish
Also, He was hungry. The same as the girl Jesus raised from the dead Luke 8:54-56
Now JWs will lead you to this verse and say that no-one will be reurrected with a physical body and inherit the Kingdom.
1 Corinthians 15:50 (New International Version)
50 I declare to you, brothers, that flesh and blood cannot inherit the kingdom of God, nor does the perishable inherit the imperishable.
However, if you check, Jesus did not use the term "flesh and blood" as He had done so many times before His resurrection but in verse 39 above, "flesh and bones". No wonder as His blood had been poured out for the sins of mankind.
Similarly, there are other groups who will says "Jesus Is Lord" but do not do the will of the Father and neither believe the scripture. The Church Of Jesus Christ of The Later-day Saints is another who come to mind.
So I find the gospel simple, John 3:16 (New International Version)
16 "For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life.
Now Jesus had quite a lot to say whist He was on the earth and later though His revelation to Paul and John etc. If you believe in Jesus, you will believe what the scripture says about Him and also want to live by His example-that is the will of the Father.
All the best,
Stephen