What according to the Bible is human nature? A simple answer is flesh and blood which man shares with the animal world (cf. Gen. 6:17; Ps. 49:12,20; Eccles. 3:18-21; Heb. 2:14). In addition, however, man is made in the image of God (Gen. 1:26; 5:1-3).
Historically the church, though denying that he was initially so, has maintained that man also has a sinful nature. And in case there is any misunderstanding at this point it contends that man is born sinful because Adam his first father was sinful. This belief begs big questions which it is worthwhile subjecting to serious if brief criticism.
First, according to Jesus man becomes the slave of sin not by inheritance but by actually sinning (John 8:34, cf. Gen. 3:6; James 1:13-15; 2:10) in his youth (Gen. 8:21) but definitely not his infancy (Dt. 1:39, etc.)
Second, Paul says that he himself was born alive (like Adam and Eve) and did not die until he, like them, had actually broken the commandment (Rom. 7:9-11).
Third, he also says that where there is no law there is no sin (Rom. 4:15, etc.). In light of this, since babies do not know the law, they cannot break it. Of course, it follows from this that they cannot earn its wages which is death (Rom. 5:12; 6:23).
(Infant Mortality: If at this point it is asked why babies sometimes die, the answer is plain. Since there is no covenant with creation (and hence the creature) which is by divine decree destructible and corruptible (cf. Rom. 8:18-25; Heb. 1:10-12), they die naturally like animals in general. Since God has made to them neither threat nor promise, they die in the normal course of nature from disease or disaster. In their case, death cannot be the wages of sin for the simple reason that where there is no law there is no sin, Rom. 4:15, etc.)
Fourth, the apostle says that we acquire our sinful nature by our disobedience (Eph. 2:1-3). This he had obviously learned from his knowledge of Adam who did the same. In other words, like Paul in the course of our development we all repeat the sins of first Eve then Adam (Rom. 7:9-11, cf. 9:11).
For, fifth, all acknowledge that Adam was ‘born’ knowing neither good nor evil. He acquired his sinful nature by breaking the commandment and as a consequence was cast out of the Garden never to return (Gen. 3:24). My assumption is that the Garden was the womb of the race. Adam was, however physically adult while we, his offspring, are genuine babies when we are born. Once Adam was outside the Garden like Nicodemus, he could not re-enter it (John 3:4). According to Ezekiel 28:13, like the King of Tyre we all begin life innocent in the Garden (or womb) till in due course unrighteousness is found in us (cf. Eccl. 7:29). It is the story of Adam repeated or recapitulated (pace Art. 9 of the C of E).
Sixth, again according to Paul we become sinful or righteous by disobedience or by obedience (Rom. 6:16) which again indicates that we follow in the steps of Adam or of Jesus, the second Adam. In the event, as flesh we are able to follow Adam, in whose image we are made (Gen. 5:1-3), readily enough but we prove incapable of keeping the law like Jesus (1 Cor. 1:29; Gal. 2:16, etc.). In light of Hebrews 2:17 we are forced to conclude that the only difference between him and us is that, though sorely tempted, he did not sin (Heb. 4:15; 1 Pet. 2:22, cf. Rom. 3:19f., etc.) while the rest of us all do (1 K. 8:46; Eccl. 7:20; Rom. 3:23; 5:12, etc.).
Seventh, if we are sinful at birth, like the leopard we cannot change our spots (cf. Jer. 13:23). So, according to Romans 1:26f., we are under natural compulsion and moral obligation to act according to our nature. If original sin is true and we are also sinful by nature, we sin by not sinning. To illustrate briefly, herbivorous leopards in contrast with bulls (Ps. 106:20) are freaks, contradictions in terms. According to Psalm 104, however, God himself feeds the carnivorous lions he has created (Ps. 104:21, cf. v.27; Job 38:39,41). In other words, animals act according to their God-given nature not contrary to it, and we are expected to do the same.
This raises the question of the future. Does human nature go to heaven? As flesh which is unprofitable (John 6:63; Rom. 7:18; 8:6-8) man is like all animals mortal and corruptible and hence cannot by nature inherit the kingdom of God (1 Cor. 15:50). However, as a believer made in the image of God he is given eternal life and a spiritual body like that of Jesus himself (1 Cor. 15:46-53; Phil. 3:21).