"He has granted to us His precious and magnificent promises, so that by them you may become partakers of the divine nature, having escaped the corruption that is in the world by lust" (2Pe.1:4). There are some people who take each verse in the Bible at its face value and treat it as an independent truth. They will find this verse to say that all we need to do to receive the divine nature is to believe in God's promises. But we need to understand that the way the Bible has been written, we need to read every verse along with all the other verses to get the full meaning.
This verse, for example, is followed by verses that tell us to add virtues to our life saying in v.8 that it is by doing so that we will ensure our being fruitful. In other words, if someone receives the promise of the divine nature and just waits for it to be given to him, he is not going to receive it! There is something we need to do from our side too.
In many cases, a promise of God is clearly attached to some condition that says if we do something God will do something. What would happen if we catch what God has promised He would do, without our doing what we are expected to do? Disappointment! But in some other cases, the conditions are not clear in the immediate context of the verses describing the promise and we need to have a broader understanding of God and His ways to see what we need to do.
One the one hand, it is the knowledge of a promise of God and our belief in it that prompts us to start expecting it. On the other hand, when we know there is a promise for us, we begin to do what ought to do in order to receive what is promised. For example, when we know that God has promised us His divine nature through His covenant of grace, we begin to expect it in faith and 1) put away all the corruption that is in us that is against His nature, and 2) learn to think and behave according to His virtues in the different situations of life.
God works in us giving us a desire and the ability to do His will, and we respond by denying all the sinful tendencies that rise up from our flesh and seek His help to do what we know to be His will (Php.2:12,13).
Human nature tends to fall to one extreme or the other, and it is difficult for us to stay balanced. Some of us just believe in the promises and passively wait for things to happen. Some others become so occupied with 'doing' that they think everything depends entirely on them. But there is a balance which we have to come to in our mind as well as in practice. Many times we learn this only after making mistakes this side or that. But we need to aim for that balance, because that is where the truth lies.
Over the centuries of Christianity, people have argued strongly on both sides. But either side does not succeed till they come to see that the other side too has a part of the truth. Finally it is when we come to find the place of balance and actively cooperate with God that we come to rest.